the issue is 

"==5940== Invalid write of size 4
==5940==    at 0x4B5B5E7: g_nullify_pointer (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4AA779A: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4B0FD35: g_datalist_id_set_data_full (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4AA78D8: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4061660: ??? (in /usr/lib/libgtksourceview-3.0.so.0.0.0)
==5940==    by 0x80770AD: ??? (in /usr/bin/gedit)
==5940==    by 0x4AA8921: g_object_unref (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4356A3F: gtk_text_view_set_buffer (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x435950C: ??? (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x808C29C: ??? (in /usr/bin/gedit)
==5940==    by 0x4AA653B: g_cclosure_marshal_VOID__VOID (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AA39DC: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AA4EB5: g_closure_invoke (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AB6704: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4ABE0C1: g_signal_emit_valist (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==  Address 0xc8d5ebc is 28 bytes inside a block of size 128 free'd
==5940==    at 0x402906C: free (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==5940==    by 0x4B32B5A: ??? (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4B32CCF: g_free (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4B470FA: g_slice_free1 (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4AC6401: g_type_free_instance (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AA8A7A: g_object_unref (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4079FBC: ??? (in /usr/lib/libgtksourceview-3.0.so.0.0.0)
==5940==    by 0x4B29AF7: g_list_foreach (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x4B29B41: g_list_free_full (in /lib/i386-linux-gnu/libglib-2.0.so.0.3115.0)
==5940==    by 0x407A87F: ??? (in /usr/lib/libgtksourceview-3.0.so.0.0.0)
==5940==    by 0x4AA8921: g_object_unref (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x409C637: ??? (in /usr/lib/libgtksourceview-3.0.so.0.0.0)
==5940==    by 0x808C3A8: ??? (in /usr/bin/gedit)
==5940==    by 0x4AAA026: g_object_run_dispose (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x43D4280: gtk_widget_destroy (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x41805BB: ??? (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x42F431F: ??? (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x41D63A6: gtk_container_foreach (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x41D7754: ??? (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x42F4B4F: ??? (in /usr/lib/i386-linux-gnu/libgtk-3.so.0.313.0)
==5940==    by 0x4AA653B: g_cclosure_marshal_VOID__VOID (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AA39DC: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AA4EB5: g_closure_invoke (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4AB6704: ??? (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x4ABE0C1: g_signal_emit_valist (in /usr/lib/i386-linux-gnu/libgobject-2.0.so.0.3115.0)
==5940==    by 0x908E09F: ???"

is there any chance you could install libgtk-3-0-dbg libgtksourceview-3.0-0-dbgsym libglib2.0-0-dbg and get a new log (you will need a ddeb source as explained on https://wiki.ubuntu.com/DebuggingProgramCrash)?