114.0b1 and daily 05-09. Recent regression, but I haven't tracked down when it started.

1. Set mail.operate_on_msgs_in_collapsed_threads = false
2. collapse all threads with \
3. single click on a collapse thread - thread expands
4. use f till you get to the first message in a collapse thread - thread expands
5. click ⌄ for either thread

Results: clicking ⌄ does not collapse/close the opened thread
Expected results: thread collapses