I think gtk+ is fubar when more than one GdkDisplay is being opened.
I am seeing hangs and crashes in gnumeric.  Since, however, that is
a large application, here is a crash example using gtk-demo.

I am leaving OS as Solaris, although I think it should be "all".

0. export DISPLAY=my-ip:0.0
1. start gtk-demo
2. select "Change Display"
3. click "open"
4. enter "mymachine:0", i.e., symbolic name of machine.
5. click on the new name.
6. click "change" and then the gtk-demo main window.
[that window goes away and comes back]
7. click "my-ip:0.0"
8. click close  [the top button called "Close" -- there are two...]
==> crash.

      ZPR: Zero page read
      This is occurring while in:
            _gdk_windowing_set_default_display [gdkdisplay-x11.c:704
pc=0xfbbdd4dc]
            gdk_display_manager_set_default_display
[gdkdisplaymanager.c:248 pc=0xfbbaa8f8]
            gdk_display_dispose [gdkdisplay.c:163 pc=0xfbb97bd4]
            gdk_display_x11_dispose [gdkdisplay-x11.c:580 pc=0xfbbdcfc8]
            g_object_run_dispose [gobject.c:466 pc=0xfb094fe0]
            gdk_display_close [gdkdisplay.c:191 pc=0xfbb97e08]
            close_display_cb [changedisplay.c:289 pc=0x601b4]
            g_cclosure_marshal_VOID__VOID [gmarshal.c:77 pc=0xfb0c3ed4]
            g_closure_invoke [gclosure.c:437 pc=0xfb08faf8]
            signal_emit_unlocked_R [gsignal.c:2344 pc=0xfb0c1d18]
            g_signal_emit_valist [gsignal.c:2103 pc=0xfb0bec88]
            g_signal_emit  [gsignal.c:2147 pc=0xfb0bf13c]
            gtk_button_clicked [gtkbutton.c:571 pc=0xfb470024]
            gtk_real_button_released [gtkbutton.c:1060 pc=0xfb472534]
            g_cclosure_marshal_VOID__VOID [gmarshal.c:77 pc=0xfb0c3ed4]
            g_type_class_meta_marshal [gclosure.c:514 pc=0xfb0901b0]
            g_closure_invoke [gclosure.c:437 pc=0xfb08faf8]
            signal_emit_unlocked_R [gsignal.c:2274 pc=0xfb0c114c]
            g_signal_emit_valist [gsignal.c:2103 pc=0xfb0bec88]
            g_signal_emit  [gsignal.c:2147 pc=0xfb0bf13c]
            gtk_button_released [gtkbutton.c:563 pc=0xfb46fe94]
            gtk_button_button_release [gtkbutton.c:976 pc=0xfb472248]
            _gtk_marshal_BOOLEAN__BOXED [gtkmarshalers.c:82 pc=0xfb585604]
            g_type_class_meta_marshal [gclosure.c:514 pc=0xfb0901b0]
            g_closure_invoke [gclosure.c:437 pc=0xfb08faf8]
      Reading 4 bytes from 0xd8