Tough to say what is going on there as we have no idea what position Chekov holds on the 1701-A (he was security chief in TMP) or if the console he sits at in Star Trek V is the navigation console. Sulu doesn't relay the order to anyone, so it could be intended that helm and navigation are controlled by one console like in TNG which was on the air at the time.
"NAV" is written on the console. When Sulu goes to change course, I think he's doing it at the traditional nav station, right? It's hard to be sure from the camera angle. So that could be the same function done from two different stations in the same movie.
I get the impression that didn't pay as much attention to details like this as they had for The Motion Picture. Just like in the original series, Sulu and Chekov's posts were kind of interchangeable.
Also, later, when Sybok is giving his address to the ship, Chekov seems to be manning both the captain's chair and his usual station, while making a remark about the ship's course.