Borticus, this was the behavior before:
1- you are in warp plasma
2- plasma dot and proc applies
3- you fire hazard emitters
4- plasma proc and dot is cleared
5- if after at the next tick you're still in the warp plasma, dot and proc is reapplied
6- at the next tick, if HE is still active, dot and proc is cleared and so on
7- if you manage to get outside the warp plasma, proc and dot is still active for an amount of time but if HE is still active, it's cleared.
Ok since last patch, point 7 of the above list is broken.
It seems to me that HE is clearing warp plasma proc while you're inside the cloud, but does not work anymore when you manage to escape.