Yo Hooj Jest Pole
Mist form from vamp runes.
Mist Form makes you invulnerable to ANY attack during a few seconds, but the conditions you had on you continue to tick.
It works the same way for mesmer and thief. You probably had conditions on your thief and not on your mesmer. Also, remember that mesmers have a bigger health pool, and the vamp runes proc at higher health, with means they are less likely to die of conditions (well, that’s not true, because most of the time your Last Refuge procs and cleanse your condis, but still).