A strange things to happen, and easily reproduced as it happens for me on both the computer and a tablet.

Pet is taken to the arena page, auto mode is set. Battles two times exactly, then the auto setting changes its self to manual. Afterwhich, if it is set back to auto, it will switch back to manual after every battle.  

Not much of a game breaking bug but worth pointing out anyways I figured.

Yes, happening to me too. 

This seems to have been resolved, hooray!