AFAICT Geany does not bind ctrl+shift+V to anything.
Looking at the traceback above (the "geany" one, the other threads are GTK/Glib internal) there is no Geany code in the traceback except the initial call to `gtk_main()` so its nothing Geany does, must be something VTE binds in GTK itself. This is probably supported by the `gtk_accel_groups_activate()` calls in the traceback.
Whilst ctrl+shift+v does always paste in the VTE here, irrespective of the widget with focus, it doesn't crash.
Not sure what else to say except, "don't do that" and bind ctrl+shift+v to something innocuous in Geany so it hopefully will hide the crashy VTE accelerator and you won't do it accidentally.
Otherwise need a GTK/VTExpert :-)