When drawing mask with pen, the final vertex is bezier by default
The net result is you can move the other vertices easily but clicking the final connection point on a shape and dragging drags out the bezier. Frustrating when you are using this feature to mask linear features such as real-estate boundaries! If this behavior cannot be fixed, how about making the vertex point interactions easier to access?
Pierre Louis Beranek commented
100% agree! It's incredibly annoying! Alt-clicking the point as Kevin suggests often results in the point's Bezier handles being reset, so it's hardly an acceptable workaround. If you click over the first point with pinpoint accuracy, then and only then will your point be Linear rather than Bezier. This is to no one's benefit and should therefore be fixed asap.
Kevin Monahan commented
Try Alt/Option clicking the final masking point. That should fix it for you.
I've found that undoing and reclicking to complete the mask a bunch of times seems to eventually work, should just by default work tho very annoying.