Well I don't know if it's a bug or working as intended, but overnight, it started to work differently.
Usually, when you cast it and mount/dismount, it's still there. However, now, I have to recast it everytime I dismount. Should I add an entry in the BugTracker?
Happened to me sometimes. Also in BG, when you die and res again, sometimes pet is gone or only the soul link buff.
This kind of thing is not really a problem, easily solved with WeakAuras. However, losing a gcd on dismount and having no dmg reduction under rogue stunlock in BG are a bit crippling.