Yesterday we found out that user System had closed a topic in a circumstance where it shouldn’t have done anything. After discarding the idea of our server reaching singularity, we found what the actual problem was. A bug that I bet you can also reproduce:
- Set a category to close topics after N hours.
- Create a topic in that category.
- Move the topic to a different category that has no automatic close settings (say, because it had been misfiled in the wrong category).
The topic remains open because it sits in a category where topics are not closed automatically.
The topic closes N hours after its creation regardless, because it carried the former category setting when moved away.
I think this bug has certain entity as described. This automatic closing from user System is done silently, and we only realized the topic had been closed after a user willing to respond complained (they thought we had closed the topic in a heavily handed moderation way).