I have modified  gnome-vfs-obexftp/osso-gwobex/src/Makefile , adding 'DEBUG' to compilation flags:

AM_CFLAGS = -DDEBUG $(am__append_1)

Now osso-gwobex logs to syslog. Here is an example log of a successful listing of a directory:

Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_LENGTH: 360 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_TYPE: x-obex/folder-listing 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: obex_readstream: got 360 bytes (360 in total) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Error or no data on OBEX stream 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:134 (gw_obex_chdir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: SetPath command (0x05) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:139 (gw_obex_chdir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:134 (gw_obex_chdir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: SetPath command (0x05) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:139 (gw_obex_chdir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_LENGTH: 677 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_TYPE: x-obex/folder-listing 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: obex_readstream: got 677 bytes (677 in total) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Error or no data on OBEX stream 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:134 (gw_obex_chdir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: SetPath command (0x05) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:139 (gw_obex_chdir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:134 (gw_obex_chdir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: gw_obex_request_sync(): looping 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: gw_obex_request_sync(): looping 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: SetPath command (0x05) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:139 (gw_obex_chdir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:134 (gw_obex_chdir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: SetPath command (0x05) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:139 (gw_obex_chdir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:159 (gw_obex_read_dir)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_LENGTH: 677 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_TYPE: x-obex/folder-listing 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: obex_readstream: got 677 bytes (677 in total) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Error or no data on OBEX stream 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:176 (gw_obex_read_dir) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:242 (gw_obex_set_cancel_callback)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:245 (gw_obex_set_cancel_callback) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:215 (gw_obex_get_capability)...
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: gw_obex_request_sync(): looping 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_LENGTH: 677 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_HDR_TYPE: x-obex/folder-listing 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: obex_readstream: got 677 bytes (677 in total) 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_STREAMAVAIL 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Error or no data on OBEX stream 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Get command (0x03) succeeded. 
Sep 12 23:19:24 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:223 (gw_obex_get_capability) 


Conversly, here's what appears in syslog in case when listing fails with the 'folder contents cannot be displayed' error:

Sep 12 23:19:44 tajwan gnome-vfs-daemon: gwobex: Attempting GW_OBEX_LOCK at gw-obex.c:249 (gw_obex_close)...
Sep 12 23:19:44 tajwan gnome-vfs-daemon: gwobex: got it! 
Sep 12 23:19:44 tajwan gnome-vfs-daemon: gwobex: OBEX_EV_REQDONE 
Sep 12 23:19:44 tajwan gnome-vfs-daemon: gwobex: Disconnect command (0x01) succeeded. 
Sep 12 23:19:44 tajwan gnome-vfs-daemon: gwobex: Unlocking GW_OBEX_LOCK at gw-obex.c:279 (gw_obex_close) 


Investigating further....