I can't help you because I think Swing and WPF are the things of the devil.
That quote should actually be at the beginning of every single book on Java UI programming handbook that has ever been written
Most likely, Swing is broken for his operating system. It can't be much else, at any rate.
Eh, don't underestimate Swing, it does provide a million ways to shoot oneself in the foot without even noticing until something inexplicably doesnt work at a random client machine...
I've run a minimalist test-case as well as a couple of applications that use Swing, and there are no issues there. Not OpenJDK and not the Oracle JRE, and the issue with Starsector is exactly the same on both (runs prefectly fine with OpenJDK btw, turned out I didnt fix library path before).
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I don't have any real idea what could be the issue here, though it appears that my initial analysis has been wrong.
The dialog is in fact fully functional and can be dismissed by clicking where the buttons should be, so there is no application freeze, just it is not properly painted.
I've seen similar issues before in a project of ours, and iirc it was due to Swing methods being called randomly instead of from the EDT.
Anyway, probably not worth examining this in-depth if it isnt an issue on other platforms as the workaround is sufficient to select mods.