How very odd.
My toolpath settings are the same, although the 'Use Radius for Feedrate' settings does no seem to matter for the display. (That figures.) But I can definitely confirm that the display only looks correct if I enter the diameter. I have played around with the X and Z DRO values to put the active point at one of the known positions, and it only matches the display when I use Diameter.
When I use the Radius the display is very obviously wrong. As I increase the value entered from 1/2 to 1 diameter, the display improves to a match. That change continues as I enter progressively larger values, greater than the actual diameter.
Could my version of Mach be faulty? Well, I dunno. It works very well on a semi-production basis the rest of the time, and the A axis works fine in practice. A bug in the code which just changes the way the radius/diameter is used for the display while not affecting anything else is a shade hard to credit.
Could it be an XML value or switch? That is always possible, given how fragile the XML seems to be. I will post a copy of my current XML shortly - it's out in the workshop and that machine does NOT have a network connection. It runs on sneaker-net.
Cheers
Roger