One block shows up for wrong nodes

A very strange problem was reported to me today. One of my users who lives very far away has reported that one of my CCK blocks is not placing correctly, and has the screenshots to prove it. I was unable to repeat the behavior here.

"CCK: Appearing In" shows information about a given node within a journal issue hierarchy. It is set, in admin/build/block, to appear on every node for every issue only, and so obviously the intent is to only show the specific field for any given node, which are all different.

My user's screenshot indicated that he was not logged in, so I tested this while not logged in myself under what I believe to be the same browser (FF3.x). For me, the correct the field is displayed in the CCK block every time for any given node, so there is no problem here. So being thus unable to reproduce the problem, I am at a complete loss, and yet I have his screenshots and good word as proof that it exists somehow.

One thought: As I was investigating today, I noticed that on admin/settings/performance, "Caching mode" was set to Normal, "Page compression" enabled and "Block cache" enabled (CSS/JS optimization were turned off). Now, I had been toggling "Caching mode" on and off throughout development, and have cleared my cached data many times, often daily, but I think Block cache" may have been on for a while. So while I doubt this could be the cause, I have now turned off all caching on that settings page and will ask the user to test once again. Not that I think this could really be the cause, since as I said I've been clearing cached data and this is (I believe) his first time visiting the site since I implemented CCK Blocks. But one can always hope.