Drunken Haze is an ability that debuffs a unit to move slower and have a chance to miss. There are multiple ways you could implement the on-hit chance proc, but the simplest would be to use the ability "Orb of Slow". Orb of Slow is a passive ability that gives attacks a chance to cast a spell on attack. You'll need to create a separate spell from Drunken Haze and set the Orb of Slow spell to cast your new Drunken Haze spell. I hope that wasn't too confusing, read over it a few times until it makes sense.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.