OK, I think I fixed it 2.24 (should have checked email instead of gaming...)
but my confidence is shattered
Here is the source code if you're interested
https://www.mediafire.com/file/tyoekyhx4xzovyc/PortraitPackEditorRe_SRC.zip/file
Viewing post in Portrait Pack Editor for Conquest
It just needed a minor change. Here's a patch: https://pastebin.com/SUsNdKn6
The only important change is to GUIFactory. The other changes were just necessary to let me build and run the project in IntelliJ.
This should be compatible with all platforms, but I suggest you give it a quick spin on Windows, particularly paying attention to the save path when you press Apply.