It's pre-season. I get a PM from another manager looking to dump a player to open up cap space. I give it a little thought and send him a trade offer, Burns (@ $500K) for Peavey (a bit over $5mil). Then I think about it and realize I may have made a boo boo.
So I go to the league page, find that the trade's been read but not accepted, and I delete it. I then send the other guy a note telling him I need to think a bit more. I push send, got back to my roster, and kabam! the trade's been processed.
Lesson learned? Don't put out trade offers you may want to rescind, as the rescind command seems to perhaps sometimes get receive more like a request.