Yes, this happened with Windows, but through iTunes. Ideally, iTunes shouldn’t have removed the filed from the iPod without warning. I can’t see why Windows is at fault here. I also have a Mac, with my sister’s iPod hooked to it. I’ll try it sometime.
I’d like to clarify that you need to delete songs from the computer from outside of iTunes for what I described, to happen.
Besides, how does one go about retrieving files from the iPod back to a new computer without resorting to dubious third-party hacks? This feature is basic in those MP3 players I mentioned. iTunes had this feature early on, but they removed it in future upgrades. This sucks too.
Actually, the iPod never had it as a supported feature (thanks to the RIAA). You can still do it, all the music is in a hidden folder on the iPod, which has never changed. It’s a little harder to find now, though - they just changed the name to something less obvious than “Music”.
The cheapie MP3 players allow you to do that because they’re not paired with a store. None of the store-linked players allow you to copy back files from the player to another computer in the same form. The store linked ones have to abide by agreements with the major labels, so no “official” copyback.