I thought so too, but a rare case indeed. We have Di2 setups at our shop and I took a look... the mechanics of the Pro Tour teams must be re-inforcing the connections at the shifters somehow because there is no locking mechanism on the plug.

I'm not trying to defend the guy. I see a plausible argument/cause..

Although I highly doubt its Di2's fault, with all that bar tape and electrical tape holdingdown the wires it should of held...

Just a tidbit of real life encounters with the stuff.