New winglets were trialled by Ducati, Honda and Yamaha in the recent Sepang MotoGP test as the teams built up the mileage on their 2018 bikes.
In this clip from Motorsport.tv's The Flying Lap, technical expert Craig Scarborough explains why a "wooly and unenforceable regulation" intended to ban such aerodynamic devices does not do so.
Scarborough looks at the Ducati and Honda designs, which were accepted, and the Yamaha version that MotoGP technical director Danny Aldridge was unhappy with.
"They've got an ever-so slightly different set-up and it's much more elongated along the length of the bike," says Scarborough.
"Danny Aldridge was a little unhappy with this design and has asked Yamaha to make some changes.
"So, Yamaha have got a bit of work to do just to make sure that they are meeting exactly what they are expecting from these regulations."