Has anyone else had file associations get deleted on their host machine?

I know this is going to read like FUD, but I'm a huge PortableApps fan and was a devoted user until recently. My hope is that someone will know something about what happened with my install so that I can get back to using portable apps again.

I'm a library school graduate student. Between my internship, the computer lab at school, classroom machines, and my home machine, I regularly use between 4 and 7 different computers a week, almost all of them XP. PortableApps has saved me dozens hours in just a few months and made me significantly more efficient than I could have been without it.

However, a couple of weeks ago, one of the machines at work lost all of its native file associations while I was using PortableApps on my USB drive. I was definitely using Firefox, perhaps AbiWord or OpenOffice, and also two portable apps that aren't supported by PortableApps, WinSCP and Notepad++. I figured it had nothing to do with my apps, because my apps don't touch the registry. Our IT guy reimaged the machine and all was well.

Then it happened again, on a different machine. There were no viruses on either machine or my thumb drive. The only thing the two incidents had in common was that I was using my USB drive on each machine when all its file associations disappeared. Fortunately, I was able to restore the file associations by following
the advice here:

http://www.microsoft.com/windowsxp/expertzone/newsgroups/reader.mspx?dg=...

But I'm not allowed to use software running from my USB drive until I figure out what went wrong. Has this ever happened to anyone else? Any idea what may have happened, how I can prevent it from happening, what I should do if it ever happens again?

Thanks,

Brett