I've been able to reproduce it with different browsers on the same computer. I'm not sure of the exact strategy, but it's just a big UX problem that I don't know what I'm sending another user.
... aaaaand now I want to make a malicious image host that always shows you your uploaded images but serves up goatse to anyone you link it to. Or maybe just flips the images, upsidedownternet style.
Anyway, thanks for expanding on it; I've shared a few images through imgur and never had this issue (maybe it was before this change, or maybe the people receiving them never complained), so I was a bit puzzled by your comment.