PowerDesk Process Remains After Exiting GUI?

I've always (10 years or so?) used PowerDesk in place of Windows Explorer (although I never choose the *replace* WE option when installing). Since installing it on Win 7, I've noticed some strange behaviour. After launching it from the start menu all is well, and when I have finished with it I close it, and its window vanishes. But if I try and run it again, it appears that nothing happens - no PD window, nothing. Try running again, again no window. Then bring up task manager an lo, there are three PDexplo.exe processes - the original that I thought I had quit, plus two from my subsequent attempts to run a new instance. I can delete one of the processes, then a second one, following which a PD window springs to life, and I can use it as normal. Again, if I exit PD the window vanishes but the process remains in task manager. I've tried running it in a couple of different compatability modes, but it makes no difference. I've just confirmed that on my regular win2k system the process is removed immediately after I exit the GUI.