Thanks for the report, I can confirm this bug, also after clicking in New file, two new files are opened, the first one without problem but the second one crash with your steps.
This is my debug log

[Nuevo Thread 0xb42f6b70 (LWP 6752)]
valide: ../../src/xcb_io.c:140: dequeue_pending_request: La declaración `req == dpy->xcb->pending_requests' no se cumple.

Program received signal SIGABRT, Aborted.
[Cambiando a Thread 0xb42f6b70 (LWP 6752)]
0x0012e416 in __kernel_vsyscall ()
(gdb) bt
#0  0x0012e416 in __kernel_vsyscall ()
#1  0x00fdde71 in raise () from /lib/i386-linux-gnu/libc.so.6
#2  0x00fe134e in abort () from /lib/i386-linux-gnu/libc.so.6
#3  0x00fd6888 in __assert_fail () from /lib/i386-linux-gnu/libc.so.6
#4  0x01184b98 in ?? () from /usr/lib/i386-linux-gnu/libX11.so.6
#5  0x01185c13 in _XReply () from /usr/lib/i386-linux-gnu/libX11.so.6
#6  0x0116aff9 in XGetSelectionOwner ()
   from /usr/lib/i386-linux-gnu/libX11.so.6
#7  0x007e04b3 in gdk_selection_owner_set_for_display ()
   from /usr/lib/libgdk-x11-2.0.so.0
#8  0x00420f9a in gtk_selection_owner_set_for_display ()
   from /usr/lib/libgtk-x11-2.0.so.0
#9  0x00502b0a in gtk_clipboard_clear () from /usr/lib/libgtk-x11-2.0.so.0
#10 0x0039fcfa in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#11 0x00326c4e in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#12 0x00b7c48c in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#13 0x00b5ecc7 in ?? () from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#14 0x00b60372 in g_closure_invoke ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#15 0x00b727b6 in ?? () from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
---Type <return> to continue, or q <return> to quit---
#16 0x00b7bb29 in g_signal_emit_valist ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#17 0x00b7bcc2 in g_signal_emit ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#18 0x004ed962 in gtk_widget_map () from /usr/lib/libgtk-x11-2.0.so.0
#19 0x004f9030 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#20 0x00b7c48c in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#21 0x00b5ecc7 in ?? () from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#22 0x00b60372 in g_closure_invoke ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#23 0x00b727b6 in ?? () from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#24 0x00b7bb29 in g_signal_emit_valist ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#25 0x00b7bcc2 in g_signal_emit ()
   from /usr/lib/i386-linux-gnu/libgobject-2.0.so.0
#26 0x004ee3f2 in gtk_widget_show () from /usr/lib/libgtk-x11-2.0.so.0
#27 0x00327c18 in gtk_dialog_run () from /usr/lib/libgtk-x11-2.0.so.0
#28 0x001c4a5c in valide_window_message (self=0x80e80d8, log_domain=0x0, 
    log_levels=G_LOG_LEVEL_CRITICAL, 
    message=0x8523328 "vala_source_file_construct: assertion `filename != NULL' ---Type <return> to continue, or q <return> to quit---
failed") at debug/libvalide/window.c:505
#29 0x001c9bd1 in _valide_window_message_glog_func (log_domain=0x0, 
    log_levels=G_LOG_LEVEL_CRITICAL, 
    message=0x8523328 "vala_source_file_construct: assertion `filename != NULL' failed", self=0x80e80d8) at debug/libvalide/window.c:1998
#30 0x00bf6b0f in g_logv () from /lib/i386-linux-gnu/libglib-2.0.so.0
#31 0x00bf6f62 in g_log () from /lib/i386-linux-gnu/libglib-2.0.so.0
#32 0x00bf718d in g_return_if_fail_warning ()
   from /lib/i386-linux-gnu/libglib-2.0.so.0
#33 0x00eb0f80 in vala_source_file_construct (object_type=224, 
    context=0x8455650, type=VALA_SOURCE_FILE_TYPE_SOURCE, filename=0x0, 
    content=0x84403a8 "pu") at valasourcefile.c:272
#34 0x00eb174b in vala_source_file_new (context=0x8455650, 
    type=VALA_SOURCE_FILE_TYPE_SOURCE, filename=0x0, content=0x84403a8 "pu")
    at valasourcefile.c:283
#35 0x015ee158 in afrodite_parser_add_source_item (self=0x8454a30, 
    source=0x844f900)
    at debug/plugins/completion/afrodite-provider/afrodite/parser.c:207
#36 0x015edf0b in afrodite_parser_construct_with_source (
    object_type=138752584, source_item=0x844f900)
    at debug/plugins/completion/afrodite-provider/afrodite/parser.c:154
---Type <return> to continue, or q <return> to quit---
#37 0x015edf46 in afrodite_parser_new_with_source (source_item=0x844f900)
    at debug/plugins/completion/afrodite-provider/afrodite/parser.c:161
#38 0x015eb591 in afrodite_completion_engine_parse_sources (self=0x83292e0)
    at debug/plugins/completion/afrodite-provider/afrodite/completionengine.c:878
#39 0x015eb04d in _afrodite_completion_engine_parse_sources_gthread_func (
    self=0x83292e0)
    at debug/plugins/completion/afrodite-provider/afrodite/completionengine.c:747
#40 0x00c172df in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#41 0x00f9fe99 in start_thread () from /lib/i386-linux-gnu/libpthread.so.0
#42 0x0108373e in clone () from /lib/i386-linux-gnu/libc.so.6