Originally the button was blank and didn't do anything, after a reload it shows a ? and still doesn't do anything. Here's the bar edit/macro text for reference, that seems to be correctish (I tried it without the ; as well, no change):

/cast Chauffeured Mekgineer's Chopper;

(I only have access to that mount on my test toon)

Dragging an ability to the bar worked fine, though.

Can you make a normal macro in the Blizzard built in macro interface for the Chopper? I'm wondering if it is a game bug

Is this for all mounts or just the one? I have no issue dragging mounts on newly created bars

Seems like just the one mount, tried half a dozen others including a couple with apostrophes and they were fine but the Chopper doesn't work.

Odd... sadly I don't have the Chopper to test lol

Hopefully no one minds, I did a bit of experimenting here without neuron active, (on alliance). It does indeed look like a game bug, since if you drag the chopper on a standard blizzard action button, the tool tip became "Summon Chauffeur". That gave me the inspiration to edit a neuron button to "/cast Summon Chauffeur", and tested as a workaround for now and the icon displays as you would expect. I will submit a bug to blizzard after I do a bit of research into whether it already exists as a known bug or has been reported. Horde does naming things a bit different and seems to work with dragging as usual.

Interesting ... Well mystery solved. I'm going to close this ticket because it seems to be out of Neuron's hands to fix it. Thanks for looking into it :-)

Confirmed, I put in a bug report with Blizzard that will be ignored along with all the rest. Sigh.