... it was the Tour des Flandres 2011.
"Depuis le Tour des Flandres, dimanche, Tom Boonen et Sylvain Chavanel ne sont plus les meilleurs amis du monde. Le Belge, quatrième à Meerbeke, s'était vite éclipsé après son échec. Il n'avait pas cru bon d'attendre le Français, malheureux deuxième et pris par le protocole."
Might have been just differently perceived in the Belgian press vs. French press...
As I recall it, he was in a small group with Cancellara and Nuyens (not alone). Both Cancellara and Chavanel were pretty exhausted from the escape they had done before and therefore got beat in the sprint. I assume Chavanel was indeed looking around to see if Boonen would still make it, but he sprinted full-out nonetheless once the sprint started (and Boonen clearly couldn't make it back anymore).
Never really heard any mention about him not beind aloud to go for it himself.
...But as I said, could just be difference in press (being a Belgian who "ordered" Chavenel to wait or because a Belgian won it and therefore took the attention away from this)
I also apologize for the thread drift... but I'm done now