I have been saying since prior to launch that it was a random duration. I never played an enchanter and never really grouped with one, but my point of reference is the Tranquil Staff.
TStaff used a similar spell except had a 100pt DD attached to it. It always only lasted a few seconds, but every once and a while it would last a long time. This was my perception of how it worked.
I know for sure it doesn't work the way it is working right now, because it is very low resist and lasts the full duration every time. Every time I have brought this issue up I have been quickly shot down and told that it is fine, don't change it. I am pretty sure it is not working as intended but the link you have provided gives some insight on the situation.
The explanation seems to say that melee combat has a chance to break the stun, which would make sense, as whenever I saw the tstaff used, it would break early all the time since you are in combat. We tested the TStaff in the beta and it pretty much made it so monks could solo anything because it proc'd all the time and permastunned the mob.
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