Got into the workshop over the Easter break and the work-around above also stopped working. Only MDI inputs would run at normal jog speed, everything else was extremely slow (cursor keys, jog continuous or step).

Was about to re-installed Mach2010 screenset, but loaded Mach3Mill instead which fired up the original Mach3 screenset. I then quit out and ran the 2010 screenset again and it was all working again. So fixed it but don't really know what caused it . . .