This probably needs to happen in the gdk-pixbuf library where the saving occurs, rather than Pinta itself
What ended up happening, if no error popped up?
Yeah, I would have assumed it would just result in an unhandled exception like the state trace you attached. If it just silently crashed that sounds like a bug in gdk-pixbuf where it's crashing in native code.
This probably needs to happen in the gdk-pixbuf library where the saving occurs, rather than Pinta itself
What ended up happening, if no error popped up?