Having written a lot of intense JavaScript of late (with many accidental infinite loops), i find that IE has the most horrid multithreading imaginable. Once a thread takes control and winds up in a tight loop, you will completely lose control - no UI whatsoever. When this happens, the screen will lock, staying blank if nothing is there yet, or even showing ghost images from other windows that are maxmized and then minimized.
Anyhow, yes this could easily be a JVM problem, or a JavaScript problem, or a browser problem. Hard to say since when the program gets hosed, the browser becomes inaccessible.