The second one is completely unrelated. I found this line in pgadmin/ctl/ctlCombobox.cpp:
#ifdef __WXGTK__ SetEditable(false); #endif
As long as I remember, we found that auto-completion does not work properly (not as expected in better manner) in the combo-box under GTK.
Hence, we decided to make the combo-box read-only at that time, until we get some proper solution.
That would explain why GTK users can't edit a combobox. The one that really bugs a lot of users is the type combobox in dlgColumn. I wonder why this specific code has been added in the first place. I found Andres added it, at revision 3562 (http://code.pgadmin.org/trac/changeset/3562#file27), but I don't find any reason why. Anyone reminds the issue? Honestly, I didn't try to remove this code and test it. I'll do tonight, but I would like to get some ideas on this code.
Thanks.
PS: I should have a complete patch for the "more complex user/database default GUC settings" new 8.5 feature tonight. I already handle successfully the database change. I'll need to duplicate it for the user properties dialog.