Java SE (Java Platform, Standard Edition)

I'm writing an application using multiple self-written JDialogs. And my problem is that sometimes the application freezes after opening a JDialog or closing it. My best guess is that the cause of this is that sometimes one JDialog launches another JDialog (because until now, that's the only time I saw it freeze) (although I have no idea how this is possible), but since I don't know it for sure, I post this question. Are there any precautions you should take when working with JDialogs (like the thread-safe launch of a normal GUI using SwingUtilities)?

Thanks,
Sam