It will still happen when you play him as other unnatural position (even accomplished position too) with natural position training.
The problem comes from playing players as unnatural position (again including accomplished status) NOT training schedule.
I've been through this problem about DR players with DL (accomplished).
This is very old issue. and I am very disappointed with SI's answer.
If this bug can't be fixed, there is no meaning of multi-position players.
Now, the only solution of this is using In-game editor . Change position status to natural, Don't try training new position.
Just using editor, because this bug will keep happening even with accomplished position.