The first mistake was opening it up to a vote in my opinion. The rules are the rules and all season the rule was the commish reviewed all trades. If you had made your stance on trades known (unless there is collusion, they're going thru) the manager(s) against the trade should provide a reason for why they believe collusion is taking place, otherwise, it stands.
Like another person said, a clear constitution is the best way to go, especially when you as commish have certain powers the league must follow.
Again, the matter should have never come down to a vote as that appears to be a rule change midseason. In the future, if you do switch to a league vote setup, the 2 owners involved in the deal should not be given a vote in the matter.
Twitter: @dmojr - Always available to talk fantasy or be that second opinion before a trade.