In tasks in lightning in the winter release there was this Mark Complete action added that we cannot remove.

The challenge with this action is it seems to get around validation rules.  ie: we have a validation rule that prevents a user from editing the task once it's moved to complete.

When a user un-marks that action the validation doesn't fire, but when we physically edit it does. 

Is anyone else seeing this?  I opened a case with support but they keep sending me documentation on how to write validation rules :/