Argument in the office today when the designers went rogue, ignoring the PM's agreed plan with the client and started mock-ups for what they thought would look better. Boiled down to "No. Just stop that and do what I asked, you're wasting your time." vs "No, we're doing this. I'm a designer, I know this will look better."

Anyone else had issues with designers trying to take charge?

Not specifically designers, but I've known people who think they know better than everyone else and can't seem to accept an alternative technical opinion nor the opinion of the actual client who's paying the money. It's one thing to pitch better ideas and I'm all for making suggestions, but another thing altogether to implement them if everyone else says "No".

Just like how people who don't code shouldn't offer suggestions on coding I think the same courtesy should go to designers.

@Letmecode that makes sense. I think if they were defending their professional integrity that'd be fair enough. From what I could gather there had been some crossed wires between both parties from a conversation some weeks ago. PM wants everyone to just keep an eye on things, does something need updating, does the design need a refresh, that kind of thing. If needs be we'd raise it with the client and go from there. The latter part just never happened.
Tbf, they're also damn good designers and know their stuff, even if it does make the work a little harder for the devs.