Ok. Turns out no user has ever asked to do that before, and since the Sim team wasn't aware of OO features and the OO team wasn't aware of Sim features, no one knew to proactively add the feature. So simulation diagrams do not support dynamic dispatching. I filed the CAR (#280810) so that it gets attention. I tagged the CAR for LV 2011, but because we are fairly late in the dev cycle for the release, it wouldn't surprise me if the fix has to wait for a future release.I'm sorry you got burned by this communication failure on our part.