we implemented quite some functionality with Java on top of Epic 4.2.1 on Windows. From time to time, we're having the problem that the dialogs open up behind the Epic window and it seems that Epic crashed. Alt-Tab is the solution to find the dialog and to go on with the work.
We call the Java methods with java_instance() instead of java_instance_modal() for performance reasons. For testing purposes, I tried to use the java_instance_modal() and got the same results.