Cannot save extension from editor Vassal 3.4.12

I cannot seem to save an extension from the extension editor in this version of Vassal (3.4.12). I can open a functional extension in the editor, and if I click on the Save button, it hangs; if I click on the Save As, it will save the file.

It feels like this is a bug. Let me know what info you need.

What OS are you using? Can you reproduce the problem with any module and extension or only a particular one?