images/pdfs in "uploads" folder suddenly missing!

I’ve been experiencing an issue with files randomly disappearing from my WP install’s “uploads” subdirectories. Not entire directories or their contents, just single files. The only thing these have in common is that they were on pages that have been updated in that time frame — is there some way they could be inadvertantly wiped upon an update (they weren’t removed from the page content — the IMG tags were intact, just showing a broken image.)

Thank God I had them all on backup, but it was maddening tracking them all down and fixing them!