Christ. Do we have some GTK person in the crowd?
The GTK combo-box entries remember old stale state even after you have first set them to first contain a single space, and then set them to contain the empty string.
Somehow they then go back in time (gtk people obviously live in some non-Einsteinian alternate universe - probably the same reality where gnome-shell makes sense) and remembers the old state of the entry field from before both of those. So when you read back the entry field, you get neither the empty string or the space, you get the previously selected entry that we have tried very hard to erase.
(Yes, we also use
to set the entry to empty, the way the documentation suggests. No, that doesn't matter either).
The hacks to just leave it with a single space (which worked from a "don't remember old state") standpoint resulted in nasty problems when editing the spinbutton entry, and the alternate hack that just replaced the space with a newline just causes ugly random "unknown character" boxes to show up with some gtk versions.
I'm fresh out of workarounds for gtk combobox entry bugs. Any ideas?