Franchise Offline Contract Question

I'm new to Madden, so I'm playing a franchise to get used to the game.

I'll try and sign players up for a 7 year contract and no signing bonus, so that I can trade or drop them and have no salary cap hit. However, I'll sign a player and they will agree to, lets say a 7 year $112 million deal with no signing bonus.
But then when I go into my player management, that player will mysteriously have a large signing bonus of $15 million or more. So if I turn right around and drop the guy I take a huge salary cap hit. Even stranger, is that sometimes I'll give another player that same contract and no mysterious bonus appears later.

Any explanations as to the mysterious bonus when during contract negotiations no bonus was given? And how to stop it from happening? Thanks