If you stop moving before you hit the ground while jumping forward, the game thinks you’re in the air forever! You can jump off a cliff, then use a Waypoint or log off without taking any damage. Also, if you just jump forward a bit and release your keys before you hit the ground, you can’t use skills or drop bundles (people get stuck on Siege Weapons in WvW this way all the time).
This is very annoying, although it seems to resolve itself after a while in low-population areas (so to test it, log out, then log in somewhere with lots of people). Thanks for your time, please fix this!