Found what appears to be a factory controller bug using 1.06 firmware.
** correction: was on 1.07 firmware **
After using the MDI interface (to set XY position), Probe Z. Then remove probe and use onscreen display to lower Z by 0.005. Set as new Z zero via onscreen.
Controller then grays out all home and setting options and disallows use of Auto reporting error ‘MDI in use’ (see screen capture).
There appears to be no obvious way to escape the MDI other than rebooting the controller - and losing the XYZ setting.
I found some similar reports of users ‘stuck’ in MDI, but not with this cause.