Overriding stuff mixed in

[Banthur]

I'm trying to prevent the pvp match results scoreboard from showing

PVPMatchResults:SetScript("OnEvent", onevents);

even with this though - the event that triggers it is still firing on the original blizzard ui code and the frame is showing

Both my function and the original are called

is SetScript supposed to replace a handler or add one?
I've also tried SetScript("OnEvent", nil) --original still called

maybe it is because the original frame is using a mixin for its handlers?
how do I overwrite or nil out a mixin's callbacks?