interesting, i have a set of st's and just went 10 speed, 10sp casetter goes on fine, as i have 2 wheel sets, a set of twe and st's, after 1 short ride, the st's doesn't shift as well as the twe wheel set so much that i can't really use the set of st's with the 10 sp....maybe that there not compatible is the reason
love to find out more if anyone got any other reasons