new positions don't stick if you take them off the training. but they should. i trained an AMC to AML (piatti iirc), so he was AMLC. i wanted to make him AMLRC, but in re-training him to AMR, he "forgot" how to be a AML. then when i retrained him to AMl (he was AMLRC), he went out on loan and came back AMLC, which was suprising, since he is a natural AMC and wasn't on position training. he is left footed, which may have had an influence.
its not a bug, just re-training positions has always been poorly implimented since cm00-01. players don't forget how to do something they've learnt.
i wonder what arsene wenger has walcott on?