There is one behavior I can't quite figure out, but I think I have an idea. When I did a hard reset, and I sync my phone via USB to my pc, some 3rd party apps gets installed automatically without me doing a thing. I think it only installs the apps that I've purchased through the Zune software on the PC. Zune seems to resync more than just songs, movies and pics, it also resyncs your apps.
I would test it to verify it, but I don't really feel like doing another hard reset