MS are trialling this new project here: http://answers.microsoft.com/en-us/feedback/forum/fdbk_commsite-mods/thread-auto-lock-feature/7c16d96b-2eb0-4bb9-93be-7b7070c64944?tm=1490385665611
In typical MS standards, this trial was started without telling anyone. It came to light when two of their most experienced & frequent contributors to the Moderation Requests & Performance Problems forums found they were locked out! Shambles.
I'm not a cynic so I won't think that the change is anything to do with wiping out at one stroke all the cries for help from those hundreds of users still waiting for help to resolve problems caused by the monthly release of flawed updates - but it's a pretty useful side-effect for MS.