PDK Ranger 9/Rogue 6. I have both faster sneaking enhancements in play with Deepwoods Stalker Faster Sneaking 3 and Assassin Stealthy 3.
When I sneak I am indeed faster than just Stealthy 3 would make me, although the PDK animation is a bit awkward, like a crab scuttling along. When I jump while sneaking the sneak speed enhancements go away after I land and I have to un-sneak and then re-sneak to get them back again.
I'm about 95% sure that this wasn't happening on a pure rogue with just stealthy.
Interesting bug if that's the case.