I noticed the same thing! maybe its a bug because I would of thought it still uses attention awareness to know your not looking at it and would only require attention when unlockingone funny thing i noticed...
i turned it off... and my phone is on the desk stand in front of me... it will not auto lock/sleep because it keeps seeing my face.. although im not looking at it...
when i turned it on ...
even im not looking at it will auto lock and sleep as per my settings(autolock 30 secs)...