I go over time with my Ts because it's their choice when to end it...it's never more than 5 or 10 minutes, but I am big on closure (even temporary; it decreases my anxiety), and therefore I prefer an appropriate stopping point if possible, and that's why they continue as well, as far as I can gather...to avoid an awkward ending and to make sure I am comfortable when leaving.
My ex-T had to stop at exactly 50 minutes past or HE would start to freak out. Which totally made me super anxious because he put the clock behind me and I always felt awkward checking my watch.
I am sorry you had such a hard time last week...I hope you can have a good talk with your T about it.