was thinking about this. Most likely its due to the following patch note:
"- Heroes will re-engage their attack target after performing an ability"
since Penitence is a ranged ability and Oak is a melee character, its possible the bug that fixes re-engaging the target has a sort of 'if out of range, do nothing' standard case. It's quite possible we will have these issues with UB Spit among other things...
.-.