Two people have reported this to Support-- http://www.insanejournal.com/support/see_request.bml?id=2293
, and I saw in the recent announcement that several other people are having problems with icons switching on them. Nearly all the users who posted about it now have broken links in their userpics. Though I suspect that the broken links used to be the misplaced icons. The second ticket I linked, that user seems to have a very obvious instance of having the wrong userpics as well as a lot of broken pics.
I left a comment on the support ticket, but figured bringing it up to wider attention would be a good idea. People who have more familiarity with how IJ stores icons might know more about why the URL paths for an icon would pick up the wrong one. I suspect that the IJ code is sometimes uploading some icons to the same real location as another user's original icon, causing it to be overwritten and thus displaying in their userpic list even though the visible path would seem to make that impossible...no one has the same user number, and all the mixed up icons have what I guess is a virtual path that ends in their user number...anyhow, I may be wrong about the virtual path, but somehow userpics are apparently overwriting others. Is it possible that the reason the user for the second ticket I posted had the trouble they did--they were uploading icons and the icons were somehow being saved with another user's user number and showing up as a broken link to them, but replacing someone else's userpic?
Sorry for the numerous edits on this and bad grammar...I'm thinking out loud in a way, so I keep coming back and editing...
This is also icon related, but I don't know if it's something that has happened a lot or if it's something that might go unnoticed by a lot of users, but one of my icon keywords changed during the move. It didn't change much; it was two words originally but lost the first word. I was able to correct it because I remembered the original keyword and changing the keyword back corrected its use. Anyhow, if it happened to me, I'm sure it happened to someone else, so if anyone happens to mention that their icons went wonky in how they're displayed in comments and such, changing the keywords for them back to the original keyword should fix it.