Well,I ran some of the old code output by V10 and it used your unmodified PP that you gave me earlier in this thread.
The spindle acts exactly as it should in that file. It regulates to initial speed and then continues steadily during that operation. Changes to the next called speed on the next op. This is as it should be.
V13 is definitely doing something different.
I thought it might had been a Mach 3 settings somewhere, but nope.
I will compare texts files and see what the difference actually is. I'll then post the results here.