The 50mm F1.4 is known have motor breakdown and recently I have realised that lens is equipped with Micro-USM and not Ring-Type USM, Canon website never state that clearly. The difference is speed...Micro USM is probably between the normal AFD motor and Ring-type.
Anyway I owned the 50mm F1.4, it is a nice lens to have but I wish for something better like the 35mm F1.4L right now.....