I have RESOLVED THE BUG!!!
The only way to resolve the bug without getting the patch is to edit the player and save the changes.
Try this: when you have all your players at one star (the bug occurs), enter the roster management, choose one player and choose edit player. Once you're in the edit player mode, just save the changes without changing anything.
Go back to the trade screen and see your player's real trade value OK again! You need to do this to the players you want to trade etc, and it works.
You can thank me later