Callum,
It should be returning the coordinate of the point on the surface the probe touched (as opposed to the center of the probe tip).
I did a quick bench test - looked ok at first pass. I set a probe up to have a diamater of 1 inch (big tip) - just to make any error from a radius comp bug obvious. I get the expected result from that simple test - but I was hand triggering the probe input on a bench set up so can't do a repeatable test to a fixed surface that way.
I really should do the real test on the machine to check this out. I'll try to schedule time to do that- but it may be a few days as I have a project that's sort of taken over the shop that I near to clear up first.
In the mean time, if the issue is repeatable, please make it occur, then grab the probing log and email it to be directly.
Log file is: C:\Mach3\MachStdMill\Logs\MSMProbingDebugLog.txt
Dave