I recently stumbled (of course) across an interesting wrinkle in Control.Invoke/BeginInvoke. From the fine print:

The [invoked] delegate can be an instance of EventHandler, in which case the sender parameter will contain this control, and the event parameter will contain EventArgs.Empty.

I dunno… While this seems to be done in order to preserve the notion of “sender” in an eventhandler, this strikes me as a somewhat shady clause to Invoke’s contract.