Helladen - we only support the Platform behavior when used with a bounding box collision mask, so we don't fix bugs unless they occur with that. Using a rectangle collision for Platform with a cosmetic sprite on top is a totally standard and far more reliable way of designing platform games.
Tokinsom - you're the only one who's provided an actual .capx reproducing the issue so far, and the link in the OP is now a 404. I can't work on this any further unless I have a .capx!