It should stack. There is no "Effect does not stack from same caster" notation in Mids nor does City of Data indicate anything other than it "Ignores Enhancement and Buffs"
http://tomax.cohtitan.com/data/power...Twilight_Grasp
Doomguide
It does indeed stack.
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I just wanted to know does the -regen from twilights grasp stack with multiple applications or does it just renew the duration from the first application?