Potion of poison neutralization says that it grants immnuity to poison for 21 seconds. Quaff it and the combat log says that Immune to trap: poison. Then (less than 2 seconds later) I run through the POISON trap in Thrall of the necromancer and the combat log says that I failed to save vs trap: poison take 76 points of damage.
THis was a test on the regular server (thelanis) after I lost a level 9 on hardcore to that trap.
Does neutralize poison grant (21 second) immunity to poison or doesn't it?