it had nothing to do with team training, beyond the fact that team training meant every player was getting training rather than just those who had played at the position(s) being trained. 10% of the training a player received is randomly assigned - i believe to just one skill. normally with only 3-6 players being trained and the amount being so small, there isn't a pop so you don't know what was trained. when training ft, stamina or game shape, all players get full training, which increases the chance the random cross-training one of them receives may result in a pop.