I am pretty sure I know what happened
In yahoo leagues under the my team page there is a link called edit my team info
If you click on this link you can change your name etc. Also there is a yes or no option for whether you can allow the commish to edit your team
The deadbeat team probably head it clicked to yes, so you commish proposed the trade and accepted it all by himself.
I guess your commish thinks he is sly
"I am ready to meet my Maker. Whether my Maker is prepared for the great ordeal of meeting me is another matter."
- Sir Winston Churchill