Aordolin, I've encountered what you experienced frequently in both OOTP5 and now in OOTP6 ('frequently' is a relative term; I play a lot of OOTP
).
It seems to happen randomly during the course of a season. I've seen it occur to guys on the 25-man roster, as well as to guys who are in the minors. I've even seen it happen to guys in the minors who were being trained at the time to play another position, different from the one that the e-mail says they now have learned.