> > It will be nice somewhere in deep clarify 
> > for experts what happens with list iterator if the list changed.

Resist the urge to over-specify.  Unless the behavior is tested and known to be consistent across all implementations, I'm content with the current docs:

"Note There is a subtlety when the sequence is being modified by the loop...."

Chris's currently patch seems reasonable to me and I don't think anything further is a good idea.

With nearly any data structure in any language, most programmers learn to be cautious about and generally avoid looping over a structure while mutating it.  Adding yet more documentation details won't make the issue go away.

I recommend posting the current patch and closing this issue to be done with it.