i never thought about flopping in this way, but it makes sense.  mine would do this while i was bonding, flop together, but on opposite sides of the room.  it makes sense when you read the description...

from the Language of Lagomorphs site (required bunny reading if you have not read it yet!): language.rabbitspeak.com/

Note: If rabbits don't get along they may play a little game one could call "I'm happier than you are." Usually when a rabbit flops near another it shows how comfortable it is with the other, but with rabbits that are not good friends it can actually be used as a mild insult. When used in this way it means something similar to the "I don't care about you" insult described later, but more like "I'm happy and you're a miserable excuse for a rabbit, so there."

oh!  aren't bunnies grand? 

Charlie used to flop actually on top of Layla, so we decided it was a combination of "I'm happier than you, you little..." and "Take that! Not feeling so tough now are you!"
We could actually hear the air come out of her as he flopped (body-slammed) her.

Also, self-grooming near a new bonding bunny translates to "Meh, I don't care about you, I care about myself. You're not even worth noticing."

I'd read that and fully expected it during bonding...never saw it but I'd thought it would be very very cute to see!!

That is so cute! I often see my two boy bunnies that are not bonded doing competitive flopping in front of each others cages. Kramer gets very creative about it, he will flop and then, to bring even more attention to himself, he will drag himself forward with his two front feet while keeping his back feet kicked out!