Yes, I've seen this also, when you have multiple images selected and click save.. some images get random metadata. I'm always submitting them one by one now.
I don't have any concrete example to report, but here's what I remember if this helps to address the issue.
When you upload images and go to the upload page, you click on 1 thumbnail and it loads the AI and IPTC. However, if you upload images and then select them all without clicking on each of them individually first in order to load the AI and IPTC, then change the category for all selected images and click save, some random metadata appears on some files.