Actually it only seems to work if the clip selected is on track one. if you'r eon track 2 for example and theres a track below that, it wont work for some reason.
I tested it on Mac and Windows and the custom shortcuts I set for Trim In/Trim Out to Playhead are working just fine.
For the life of me I cannot get it to work 100% of the time. It's oddly hit or miss. I have a clip selected, i even have the track selected, and.. I dunno.