Turns out, it was reported before, but without much clue how to reproduce it, without even a proper backtrace. So I left a comment.
Oh, nice, found a workaround: assign it to the org-level "iocaine 4.0" project after opening the PR, not while.
That's better than using AGit PRs in this case. I love AGit, but in this case, the branch to merge is already in the repo, isn't from a fork, so AGit buys me nothing, but makes it harder to explore the branch.

kura ist ja heute sehr musikalisch