Ever since beta tumble has been broken slightly, and it still drives me insane.
When you tumble at any skill level left and right, you will always tumble farther left then you will right, therefore sometimes tumbling you off a cliff by a few millimeters.
Testing: Stand on a tile with a unique marked location so you can tell where you started from, tumble left then right ~10 times, check the distance you are from the "starting" location.
I know its not something tremendously important, but this has been around since beta testing, and still not fixed