The 10 speed hood have a nub that fits in a notch on the shifters, keeping it solidly in place, with no gaps. There are those tab things on the 11sp hoods...
Maybe an install issue?
Comp Cyclists says this on installing them:
As with all ergo hoods, there's a right and left. If you are replacing a fatally damaged hood, cut off the old hood and put this one on by threading it over the bottom of the brake lever blade. Bring it up and over the knob at the top of the lever and then down into place. Do not grab the thin end or little tabs. Try to pull from the meatiest part of the rubber. While technicians at Campagnolo tell us not to use lubricant, we've found that rubbing alcohol provides plenty of slipperiness between the rubber hoods and the lever bodies -- just like sliding on mountain bike grips. You'll have to wait five or ten minutes for it to evaporate before you ride. Campagnolo 11-Speed Ergopower lever hoods only work with Campagnolo 11-Speed Ergopower levers.