We just upgraded to 2.8.0 and TL4’s can’t undelete their own posts.
I mean, they can as long they don’t refresh the page: once they do, their (deleted) post no longer shows on the topic and it is not behind a “view hidden posts”. Staff can still see the deleted posts (within the 24h), just not the post author. This seems to happen only with TL4 as far as I tell, but I only tested versus a TL2.
Not sure if relevant, but I reported this same issue last year when we upgraded to 2.7.0 and a fix was done. But, we never got around testing that specific bit as it wasn’t back-ported and the original (security) report had been about another issue (also related with TL4’s) that was addressed on 2.7.5, so we only tested that part.
Anyhow, in short, TL4’s can’t undelete their own posts on latest stable.