I can't reproduce the crashes but there is a glib warning:

GLib-GObject-WARNING **: instance of invalid non-instantiatable type `(null)'
aborting...

Program received signal SIGTRAP, Trace/breakpoint trap.
IA__g_logv (log_domain=<value optimized out>, log_level=G_LOG_LEVEL_WARNING, 
    format=0xdf5c38 "instance of invalid non-instantiatable type `%s'", args1=0xbfffe8bc "")
    at /build/buildd/glib2.0-2.21.6/glib/gmessages.c:512
512	/build/buildd/glib2.0-2.21.6/glib/gmessages.c: No such file or directory.
	in /build/buildd/glib2.0-2.21.6/glib/gmessages.c
(gdb) bt
#0  IA__g_logv (log_domain=<value optimized out>, log_level=G_LOG_LEVEL_WARNING, 
    format=0xdf5c38 "instance of invalid non-instantiatable type `%s'", args1=0xbfffe8bc "")
    at /build/buildd/glib2.0-2.21.6/glib/gmessages.c:512
#1  0x07e89056 in IA__g_log (log_domain=0xdf093c "GLib-GObject", log_level=G_LOG_LEVEL_WARNING, 
    format=0xdf5c38 "instance of invalid non-instantiatable type `%s'") at /build/buildd/glib2.0-2.21.6/glib/gmessages.c:526
#2  0x00de0ce3 in IA__g_type_check_instance (type_instance=0x8247bc0) at /build/buildd/glib2.0-2.21.6/gobject/gtype.c:3807
#3  0x00ddbae6 in IA__g_signal_connect_data (instance=0x8247bc0, detailed_signal=0x8085240 "contact-presence-changed", 
    c_handler=0x806e910 <event_manager_presence_changed_cb>, data=0x82475b8, destroy_data=0, connect_flags=0)
    at /build/buildd/glib2.0-2.21.6/gobject/gsignal.c:2238
#4  0x0806e7ca in empathy_event_manager_init (manager=0x82475b8) at empathy-event-manager.c:1059
#5  0x00de93bf in IA__g_type_create_instance (type=136096560) at /build/buildd/glib2.0-2.21.6/gobject/gtype.c:1674
#6  0x00dccd38 in g_object_constructor (type=136096560, n_construct_properties=0, construct_params=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1338
#7  0x0806e55b in event_manager_constructor (type=136096560, n_props=0, props=0x0) at empathy-event-manager.c:973
#8  0x00dcd8cc in IA__g_object_newv (object_type=136096560, n_parameters=0, parameters=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1215
#9  0x00dce502 in IA__g_object_new_valist (object_type=136096560, first_property_name=0x0, 
    var_args=0xbfffecf8 "`{$\b\364\17", <incomplete sequence \340>) at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1278
#10 0x00dce67e in IA__g_object_new (object_type=136096560, first_property_name=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1060
#11 0x0806e39b in empathy_event_manager_dup_singleton () at empathy-event-manager.c:1066
#12 0x0807dfb6 in empathy_indicator_manager_init (manager=0x8247b60) at empathy-indicator-manager.c:333
#13 0x00de93bf in IA__g_type_create_instance (type=136096296) at /build/buildd/glib2.0-2.21.6/gobject/gtype.c:1674
#14 0x00dccd38 in g_object_constructor (type=136096296, n_construct_properties=0, construct_params=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1338
#15 0x0807de6b in indicator_manager_constructor (type=136096296, n_props=0, props=0x0) at empathy-indicator-manager.c:290
#16 0x00dcd8cc in IA__g_object_newv (object_type=136096296, n_parameters=0, parameters=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1215
#17 0x00dce502 in IA__g_object_new_valist (object_type=136096296, first_property_name=0x0, 
    var_args=0xbffff088 "\b\33\"\bP\350!\b") at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1278
#18 0x00dce67e in IA__g_object_new (object_type=136096296, first_property_name=0x0)
    at /build/buildd/glib2.0-2.21.6/gobject/gobject.c:1060
#19 0x0807dd6b in empathy_indicator_manager_dup_singleton () at empathy-indicator-manager.c:246
#20 0x08075ccb in empathy_main_window_show () at empathy-main-window.c:1258
---Type <return> to continue, or q <return> to quit---
#21 0x0805bb91 in main (argc=1, argv=0xbffff434) at empathy.c:868

Not seeing why this is occurring though..