>if I visit a folder and see some files, I know what I see is all of the files there (+/- hidden file settings); if something is missing, it's not there, period.

Funny you should say that. Only a few weeks ago a colleague of mine was perplexed by a file which showed up in a 'save as' box, but not in Windows Explorer. It was an ordinary log file, same as a bunch of others in that folder, no reason for it to be different. Apparently he later discovered the file was visible if navigated to from C:, but not through the desktop shortcut he'd made to that folder. We could only conclude it was a Windows bug. Whatever the cause, it wasted a good deal of our time hunting for that file...