After today's train I noticed that the "page" field on Special:Abusefilter has become mandatory. This means that users can't test filters the way they want, but instead they have to add a page, which sometimes could make testing unuseful. This bug does not come from AbuseFilter, since on my local wiki using the master I don't have it. Instead, it's more likely to come from either OOUI or HTMLForm. Further investigation coming.
Okee doke! Are either of you familiar with the SWAT process? We need to schedule the change for deployment at https://wikitech.wikimedia.org/wiki/Deployments#Week_of_May_14th, and be on IRC at #wikimedia-operations during that time. You'll probably be asked to check the debug server before the changes are synced. I'm confident enough in that patch to serve as the deployer or responsible developer but I won't be able to do it until the evening SWAT window at 23:00 UTC.
The issue is known, it's not caused by AF and is already fixed in the master. It wasn't deployed due to Echo test fails which are blocking patches on past branches. Unfortunately, unless those issues are fixed, we'll have to wait for the next train.