A foreseen rule change to the rear fin of F1's 2018 cars has been opposed by McLaren, and complicated its rivals' design work at a very late stage.
Teams discussed retaining this year's large rear aerodynamic engine cover at last Tuesday's Strategy Group meetings.
Preserving the large surface is seen as beneficial to sponsors and also to the FIA's desire to see larger race numbers displayed on the ubiquitous engine cover.
McLaren, who would like to see a reduced rear fin, did not vote in favour of the proposal which requires unanimous support to go through.
The Woking-based outfit apparently vetoed the change as it believes a smaller engine cover would improve the visibility of its rear wing, and the presence of its sponsor.
McLaren's Eric Boullier also argued that a smaller rear fin would perhaps better serve the interests of its 2018 design.
"Maybe we have found a way to use the engine cover that works better," he said.
"The cars are complicated today so it is difficult for Zak [Brown, CEO] to find big stickers.
"But we are not playing games. Everyone is developing their own car so if you ask for something which is against our interests, I will not go for it.
"Some teams have tried to play something that was more suiting their car model, or whatever. But we have a regulation in place for next year, so if there is no unanimity then there is no reason to change."
While a compromise will likely be sought, teams could face a serious design conundrum at a very late stage of the process.
"We have to release an engine cover soon, it would be nice to know the rules," said a frustrated Otmar Szafnauer, Force India's COO.
"I thought we had it all agreed. McLaren, I believe, wanted to expose the rear wing more, but the rear wing isn’t exposed only because it sits so low now.
"That is why you cannot see the sponsor. More so than because of the fin.
"The fin hides it from certain angles but not from head on – you can’t see the fin from head on. You cannot see the rear wing because it is so low. For us it removes a pretty big area for the sponsors."