Ken - many thanks for your explanation of events.
1 - the bug. This was a basic operation so the good news is that failure wasn't my fault. It would be useful for me to know what to do to avoid the circumstance (what-ever it was) re-happening....
2 - the guiding is down to me. I misunderstood something else here. I edited this para a few minutes later but should have deleted most of it. Some options are still not understood by me.
Generally I wish I could interpret the logs better! Still can't see how far off the first 'goto' was, even though the plate solved.
Thanks again
Lawrence