Same thing here. I’ve been having this issue since Cubase 7.5. I switched to 7.5 from Cubase 6, skipping 6.5 and 7 versions, so it’s hard to track back where it appeared first.
In addition to that problem with the last hitpoint being inactive, auditioning hitpoints works strange. Normally you can left-click to the right of any hitpoint and it plays back the piece of audio after this hitpoint. But when clicking to the right after the last hitpoint (after you manually activate it), it doesn’t produce a proper sound - just a sustain tail.
There’s a little hack with auditioning it: if you click to any previous piece of audio, and then quickly click to the last one, it will sound right. But only if you do it quickly. Perhaps, this behaviour can be the key to fixing this nasty bug.