Don't allow teams that are involved in a trade to protest their own trade.
All trades that I have accepted or proposed which were accepted still show the "protest trade" button/option on the bottom of the pending trade page even though I am one of the teams that accepted or proposed the accepted page. This shouldn't be allowed for teams that originally agree on the trade, only for other teams in the league.
I recently had a trade that was accepted where the owner who accepted the trade, protested their own trade after a day or so when news came out about their injured player they were trading was going to be back sooner than anticipated. The other manager admitted what they did and when combined with another veto or two from other teams, someone at Yahoo vetoed the trade at the deadline, even though it was a fair trade, between a 1st and 3rd place team no less?