I think the training of a transfered player doesn't change back to a default. It stays the way it was at his former team.

For example:
Team A trains a QB at punting
Team A sells this QB to team B
Training on QB at team B is punting


I think training should be changed back to Attacking - All skills in this case.
In case the natural position of a player is:
* offensive, training should be set at Attacking - All skills
* defensive, training should be set at Defensive - All skills
* special, training should be set at Kicking - All skills


Just my 2 cents