SOLVED: (Me) Why G55G90G0X-6.88 ends at X-19.15??

[Summary: in all the efforts to get this new machine up and configured, I had forgotten that one of the things I had been working on was "auto-tool-height-setting" whenever an M6 is encountered. I discovered this, not by stepping line-by-line through the program, because AXIS' status window doesn't identify the current location but, by sequentially copying one line at a time from the offending program into a new much shorter one--until the new program "failed" the same ways as the old--on the M6 Tn line. That's when the light bulb came on. I'd have recognized it sooner too, but weeks have passed, and I had been working on a smaller piece, where the coordinates of the "phantom G38.2" were 'off-piece.' In the latest work, those coordinates are still over the workpiece and as a result I didn't recognize what was happening. As I wrote: "too big to see." However, I told Ghost-busters they could stand down...]

Running 2.7.6 on Ubuntu 12.04LTS.

I'm trying to troubleshoot a program on a new machine which is baffling me. It's something simple no doubt, but too big for me to see it.

I have homed the machine (and G54 to lie on top of G53). I have moved to right front down of Home and touched off XYZ=0 in G55 to define its origin.

I have loaded the program for which you see a snippet attached.

The first move (snapshot is attached) is G0 Z0.5 which happens to be up is executed, but that occurs AFTER M6 and M3 are ignored, and is immediately followed by a surprise G0 move to X-19.1565Y-0.4337.

Thinking that there was a residual G92 (although I do not use it), I added a G92.1, but the bizarre result is the same.

When the machine reaches its self-decided X-19Y-0.4 location, it immediately plunges, again ignoring M5 and M2 commands to do so. You'll notice that it plunged beyond Z-0.006 before I hit Escape.

I believe the (STOCK,), (TOOL,) lines are inserts from MeshCAM, and I should say that I used 2.7.5 with similar MeshCAM output for years on the old machine, and in fact they are merely comments.

I realize I must be doing something dumb, but I just can't see it. (Did I leave the parking brake on?)

Thanks.

Continuing to look for clues, I found this, which is no doubt relevant:

The offset from G53 X0Y0 to G55 X0Y0 is X+11.1565 Y+0.4337 so the initial surprise move to G55:X-19.1565Y-0.4337 is equivalent to a G53 G90 G0 X0Y0.

I just cannot see WITW my code is asking for that!

[EDIT: because, as a result of my earlier forgotten efforts, it's a hidden part of processing an M6 Tn command... sigh]

I have reduced the program to the lines following, but stepping through it is not enlightening because my AXIS display does not indicate which line number has executed. None of the (MSG) lines are displayed. When I hit the Run icon, it shot through the program, ignoring the M0/pauses and--I kid you not--arbitrarily sets coordinates to X-8Y0, runs a probe and errors out with the error message "G38.2 move finished without making contact."

Erm, no G38s in this code. [No, but...]

Is 2.7.6 smoking crack? [No.] Maybe something got into my Froot Loops? [EDIT: 2.7.6 is fine; it was my sorry memory.]

I left something out again. The latter "tests" with the trivial program were run remotely (via 'ssh -X' to the controlling computer) and the CNC machine was not on.

However, although LinuxCNC remembered the relative positions of G53 and G55 origins, no homing commands were issued (in order to keep it that way, because the CNC was not powered). The program was thus run in simulation mode: I have not verified whether LinuxCNC will run a phantom[1] G38.2 in "live" mode--and I'm not looking forward to testing.

Figured I'd better add this information for completeness' sake.

[EDIT: [1] Phantom indeed in that it runs as part of a hidden tool-height setting routine I previously set up and forgot about.]