Java SE (Java Platform, Standard Edition)

I have a problem that pops up on rare occasions in my Swing app, and I would greatly appreciate thoughts on what might be happening (I'm having a very hard time troubleshooting because it only happens on very rare occasions). Basically, in the course of using the application the mouse cursor starts displaying the window resizing icon (the vertical up/down arrow) yet still functions as a normal mouse cursor. When this happens nothing I do causes it to revert to the regular arrow, but it will display the other icons when appropriate. I'd post code, but I haven't the faintest clue where the problem exists.

My only guess is that it has something to do with the heavy amount of threading going on in my application (a lot of images are being loaded in the background, but I'm fairly sure that all Swing objects are only being used in the event thread). The other possibility is that my use of the Substance LAF is contributing to the problem. I haven't experienced the problem without the LAF, but as I mentioned it only arises very rarely so this may be coincidence.

Any tips on how to troubleshoot this problem would be much appreciated.