From reading all the comments I am seeing the following - There are people on the forum who are unaware of a method of exploiting in the game. I will not go into the specifics of how this method worked but the focal point of it was the use of the Goalkeeper Drill.
For the longest time this drill was used by many out of simple convenience (What rogerniceguy explains in his post), but the fact is that in reality this drill was abused to circumvent the intended design behind player training.
All of this is being fixed now. And to repeat myself from my earlier post - Point 3 of the changelog is about a similarly-working method of cheating. Those who've used this one will be well aware what this change means.
EDIT: I should also add - The Goalkeeper Drill is finally working as intended. Let that be well known. If you open the drill and take a look at the attributes it covers, you will find that all of them are only present in the Goalkeeping skill that only Goalkeepers have. Furthermore - All drills use up Condition, it doesn't matter if the player can or can't gain anything from the drills, he will still pay with his Condition stat. That is why SausyFC recommends that you don't add this drill to mixed-player training sessions (well unless you put your GK in the list with them ofc, and even then only he will benefit from the drill).