The wings of McLaren and Mercedes in particular have drawn attention over recent races for apparently flexing more than the spirit of the regulations allow, but each have passed the standard FIA load-bearing tests. 

Wings will always flex to create more downforce as they are loaded with the forces of a grand prix car, with certain tolerances built in, but Red Bull advisor Helmut Marko wants to see greater investigation into the McLaren and Mercedes designs.

Sour grapes…

Reb Bull of all teams complaining about other teams' wings that flex but pass the flex test is pretty funny, considering they absolutely blew their lid when they were accused of it not long ago.

Still, this is just the nature of being an F1 team principal. Bitch and moan about any aspect of other cars that you can.