(edited by Icarus.1728)
Stability Bug
Immobilize (also including what I assume you mean by rooting, the Ranger skill Entangle) is not prevented by Stability, that’s intentional.
A Necromancer skill, Corrupt Boon, can be used on players with Stability, and it converts it into Fear, that would explain why you are being feared out of Dagger Storm.
Not all skills that break stuns provide stability, lots of them break any stun you’re currently in and that’s it.
If you have video evidence of being knocked down or stunned while you have stability up, that might shed some light on the situation, because while you say it happens to you all the time, I’ve never had it happen to me, and I’ve never seen that happen to other players.
This is not exactly the OP’s problem, but i noticed some kind of race on a few skills that break stun and grant stability: When you use the skill and get stunned around the same moment, you can end up with the skill on cooldown and stability up but you are stunned nonetheless. Obviously this should not be possible, if the stun break and stability effect occur atomically.
It happened multiple times already and i think it was with both, “Stand Your Ground” on Guardian as well as Balanced Stance/Dolyak Signet on Warrior.