I mangled a convert to comment earlier and needed to undelete the post so I could redo it. When the post was converted a second time, I noticed it suddenly had a single undelete vote (it said "undelete (1)" on the link, and showed up in the 10k list). When I undeleted and converted it again it had two votes, and so on:
If I delete normally it works fine; it's only converting to comment (and probably edit, although I didn't try) more than once that leaves behind undelete votes