There seems to be more to this, perhaps related with TL4 permissions.
– As an admin: I created a new topic, then moved that single post elsewhere. Went back to the stub topic, changed the 7d timer to a minute from there. After some minutes the background job marked the topic as deleted. This is the intended behavior.
– As a moderator: repeating the steps above works just like with an admin account.
– As a TL4: I repeated the same steps. But, after the (reduced) timer expired, the topic remained there (not deleted) and the timer disappears from view.
I believe a TL4 normally can’t create an auto-delete timer, although they seem to be able to edit it in this case (the countdown does change!), even though it ends up not deleting the topic. So perhaps the bug is that TL4s shouldn’t be able to edit topic auto-delete timers?
As evidence that there seems to be something amiss with auto-delete timers and TL4 accounts, I noticed this oddity: once the stub topic (reduced) auto-delete timer expires, if they go to the Set topic timer..., this shows:
Note the deleted selected entry. But opening that dropdown, it’s not even one of the options:
In short: the issue seems specific to TL4’s editing stub topic auto-delete timers. They seem able to edit the timer, the countdown appears to change, but the topic is not deleted on the new date.