The problem here was not in XSetErrorHandler (that was not needed anyway at this point), but in the call `QGnomeTheme::themeHint(hint);`
I don't remember the details now, but it was somewhat caused by some code in gtk2 yes.
Upstream qt has not this kind of issues. Also gtk3 is not X11-only toolkit, thus it self-protects when not running in such environments
The problem here was not in XSetErrorHandler (that was not needed anyway at this point), but in the call `QGnomeTheme: :themeHint( hint);`
I don't remember the details now, but it was somewhat caused by some code in gtk2 yes.
Upstream qt has not this kind of issues. Also gtk3 is not X11-only toolkit, thus it self-protects when not running in such environments