With focus specc (no unremtting) i have been pulled back "mid-air" plenty of times. Not sure if you got your facts straight, only reason it wouldn't work would be if i was whitebarred or otherwise immune.
You both might be right. As a PT myself, I've seen my grapple rendered useless plenty of times by leaping guardians. Resolve is out of the question, I don't pull if I see the white bar. The way I see it, it's a matter of who does it last. If the guardian leaps first, you can pull him back, if the pt pulls, the guardian can leap and cancel the pull.
There's also the lag factor that could make it look like they both happen at the same time with one taking priority over the other.