Sometimes a wiki has patrolling on and then decides it's not useful for their purposes and turns it off. This results in a whole lot of patrol log entries that most nobody wants to see suddenly becoming visible in the log with no way to effectively hide them. (Because apparently the filtering thing $wgFilterLogTypes doesn't apply to it anymore, or something, though you can still select it in the dropdown as a type to only show.)
It's kind of annoying, although obviously not something that would come up often.
But when it does it's kind of annoying.