Great, thanks for that!
I’ve uploaded a fix in the source code link you used (the link mentioned in this post). It’s the same download link but with updated source code. The only changed file is src/qt-widgets/SaveFileDialogImpl.cc (so you can just replace that one file for a quicker build).
For others reading this, the bug happens on Linux only (including Ubuntu) but not on Windows or macOS.
Regards,
John