Odd transformer behavior

[badman]

I have a 1:1 transformer wired up as a phase switch: the secondary is simply reversed via switch to invert absolute phase. However, one setting is dramatically better, seemingly outside the realm of absolute phase differences- dead treble, etc. And I mean dead.

Any ideas? It's wired correctly and in place between my linestage and active XO. The only thing I can think of is some goofball ground shunting.

[badman]

I was switching the secondary. Needed to be the primary, secondary is asymmetrical. I'll test switching it around.

[badman]

No luck

[Stocker]

parasitic capacitances and inductances are hurting you