Why did the lathe take off 6 thousands when the cross feed was indexed at 2?

I was broaching a 1911 frame, even it had .003 of spring. I will know better for next time. This is not just known to lathe work.
 
As I believe someone else also said, simply make sure your final 2 passes are the same DOC. If I was turning 1.5 down to 1.0, I would take roughing passes down to 1.05, check my diameter, dial in half the remaining, make the cut, measure, and make my final pass, so, for instance, my diameter progression might be 1.5, 1.4, 1.3, 1.2, 1.1, 1.05, 1.025, 1.000. Doing this, I can generally hit well inside of .001”, with no spring passes. The key is that your final two cuts need to be the same. Don’t sneak up on it.
 
I think you introduced error when you zeroed the cross slide dial then used the compound to 'touch' then went back to the cross slide to dial in the cut.
The venerable Tony Foale posted the following about making fine cuts and it is one of those "Why didn't I think of that " tips that is a job saver.
 

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  • Improving lathe turning accuracy. - T. Foale.pdf
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Where is the original poster? Second page and nothing from him. Not cool.
 
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