Another reason I bring fixtures up is that I do not use Mach or Linuxcnc as my controller. I use Turbocnc and it defaults to G53 on power up so when I used the test case last night, if I ran it on the machine, it would be in G53 until it hit the modified code portion after the probing sequence. I can easily put G5x in manually until you get it sorted out.
And if anybody else is reading this and wants to use Turbocnc, I have a customized version that captures the probing position for use in this software.