Strange GObject warning, crashes GUI

[John Coppens <john jcoppens com>]

Hello people.

While updating an old program, warning messages started to appear
each time a ComboBoxEntry dropdown button was pressed:

GLib-GObject-WARNING **: gsignal.c:3081: signal name `depressed' is
invalid for instance `0x89c8e0' aborting...

This seemed innocent enough, so I tried to run the program with
--g-fatal-warnings in gdb. The program ran fine till the dropdown
button was pressed. Then most of XFCE blocked completely (only the
clock was updating). No closing windows, no changing desktops...

Of course, no debugging info either. I googled this error, and found a
few instances of the same problem, but this was ignored by all
responders.

I was using gtk+ 2.20.1, glib-2.0 2.27.2...
I suspected a problem with glib 2.27, so reinstalled 2.26.1, same
problem.

Now compiling gtk+ 2.22.1...

I'd appreciate suggestions...
John