Conditions tested on:
Windows 7 Ultimate (latest)
Press S (to fall through) until you can't fall through a normal FT platform.
The bug occurs very frequently but I don't know the exact reproduction conditions so it's possible to make it to the bottom w/o seeing the bug.
Press ESC to restart layout in this instance.
Given the provided Capx, it is possible to land on a floor yet C2 is saying that the Player is not the on the floor. I believe the action pictured below is the culprit as it doesn't occur when I disable that particular action. As such, I assume that the bug is occurring because the collision polygon disappears for an instant while the animation is changing.