You mean increase in lap times?
On the community RBR forums, one of the team mechanics said this was rubbish. He stopped at the end next to a firemarshals post. Also, if it was a fuel thing, you do what Massa did, gradually slow it down, and you give the driver a constant stream of information about how fast/slow he needs to go. We got none of that, just Sebvet asking if there was anything that could be done to fix it.
As for design flaw, Webber was fine and from what we've heard he uses a touch more fuel than Sebvet.
http://www.patronisef1.com - My solution to F1's 'bore' problem.