Similar thing happened to me years ago in an almost stock TT. The HICAS went bananas after a quick WOT lane shift and the back wheels kept turning even after I straightened the car out. Corrected about 6 times to no avail and eventually jumped the curb / spun off the road. Thank god it was an open field over the curb...
93 2+2 Twin Turbo Track Build - jsworks.org for more info!