unless I am mistaken, a Automatic has a computer that controlls which wheels get the horsepower through the transmission, making it so if there is no resistance on a given wheel, the others get the horsepower.
In a manual transmission (which you and I both have) it gets a bit more tricky
as nearly as I can tell (just from how it feels), the car has a center limited slip differential and/or a limited slip on each axle
basically this is hardware (gearing) that makes it so if one wheel is slipping it gets no horsepower. I THINK that it is possible for both back tires to grip, while both front ones spin, which would be what happened to you...
I asked my local subaru performance specialist this question, and I got a blank stare...
sorry I even posted, I think I raised more questions than I answered...
