Mine does the same and I think it's the single most annoying aspect of the car. It's so pronounced that it requires minor steering corrections. To me, it feels exactly like power is being distributed alternately between the rear wheels and the car is being "steered" by the difference in power going to each wheel.
BTW - I have 265 non run flats in the rear and it doesn't seem to make much difference whether DTC is enabled, partially or fully disabled. I honestly don't see how some of these guys running tunes, meth, full bolt ons, etc can stand to drive it this way.
From what I've read, it can be remedied with an LSD and an assortment of M3 suspension parts. I honestly don't think I have the resolve to sink another $3k-$4k into it at this point.