Oh poo; I'll stop offering that as advice then. It would be nicer if they just left cleared keys cleared until such a time as the player clicked "restore defaults".
This is expected behaviour for me.
This does not always work. As I've reported in the past, some keys keep resetting regardless. For example, I keep reassigning Q/E to control the camera, but every time I restart the game, E once again opens the character screen (as well as swirl the camera, at the same time).
And in his example, he rebinds X to Sneaking, just to see X rebound to some GM option upon restart.
I have the same problems with the same key bindings
