This is the bug:
Upon refreshing corruption with EA, the spell power coeffiicent of corruption drops from 186% to 159.6%. Or, as the devs like to put it, drops from a .31 coefficient per tick to a .266 coefficient per tick.
What's happening is that when EA refreshes corruption, the DoT's base coefficient is reverting back to 93.6% or .156 per tick.
See the above thread on the WoW forums for the testing I did to discover this.