Mechanical broad head

I shoot a Hoyt havoc xt 2000 (or something along that line) and recently shot a small doe at 30 yards, firstly I noticed poor penetration even though it was a decent shot, should have been a lung/heart shot.... Luckily the deer was mortally wounded and died in sight. However on examining the arrow, it appears my mechanical braid head only had one blade open.... Is this common? I suspect a slightly worse shot wound have only wounded a bigger deer, and that's not what I am after! Clean, quick kills.

What type of Mechanical broad head are You using? I know You said poor penetration, did the broad head make it through the deer? some mechanicals look like the blades didn't open after coming to an abrupt stop and closing a blade or two. Did the wound show only one blade open?

I think the broadhead probably opened if the deer died within sight. Also when they hit the ground or hit anything hard they will close back.