This is just something which spooked me out. PC #1->plugged in USB HDD, removed it, plugged into PC #2 modified file structure + edited a text file on it on a different PC, plugged it back in to PC #1.
The old file structure was still there, and the text file was the old version.
Re-plugged into PC#1 and the new stuff could be seen (although I don't know what was different about the replug)
I'm curious, I suppose it cached stuff from the USB drive and worked from the cache, but this must be quite a persistent cache, and how do I know when I'm working on the Cache? How do I clear the cache if I want to be sure what I'm looking at?