I have all 3 ranks of faster sneaking from deepwood stalker and when I enter sneak, it's working fine, my movement speed is increased.
If I jump however, my sneak speed after landing is slower, as if I didn't have the enhancement.
If I toggle sneaking off and on again, faster sneaking kicks in again.
If I tumble, faster sneaking starts working again.
It seems to be falling for any distance that makes your character use the falling animation (arms out wide for non-monks) causes it to stop functioning.
Featherfall doesn't make any difference as far as I could tell.
My jump skill is -9 while sneaking, if that makes any difference.
Has anyone else seen this?