Fear STILL removing Stability
That has happened yes, and it has proc’d as it states, but other times it has not. It has been his mark while using the staff. I have a necro as well so know the skill. It also does not explain at all why Warriors are able to do it as well.
I know as well too that it is no the corrupt boon for the simple fact that the switfness and regen that are on the bar are not converted into conditions.
The feature patch “buffed” Fear so that it is now a full interrupt (like dazing and several mesmer skills). Additionally, it may be a result of traits. One such trait is a triggered Spinal Shivers cast when hitting something 50% or lower. It strips boons in the process.
Additionally, if there are minions around, they may have had the trait that grants minions a chance to strip boons on hit.
http://wiki.guildwars2.com/wiki/Sigil_of_Nullification is how a warrior(or anyone) can do it. It also got buffed/fixed so that it will only proc if there is actually a boon to remove.