Well, I think we can conclude that it's expected by *them*.  :-)  I
still find it surprising, and it somewhat lessens the utility of
re.split for my use cases.  (I think re.finditer may also suffer from
the same problem, but I don't recall.)

If you look at the comments attached to the patch for this bug, it
looks like akuchling and rhettinger more or less saw this as being a bug 
worth fixing, though there were questions about exactly what the
correct fix should be.

http://bugs.python.org/issue988761

One comment about the your doc fix: You highlight a fairly useless
zero-character match (e.g., "x*") to demonstrate the behavior, which
might leave the user scratching his head.  (I think this case was
originally mentioned as a corner case, not one that would be useful.) 
It'd be nice to highlight a
more useful case like '^(?=S)' or perhaps a little more generically
something like '^(?=HEADER)' or '^(?=BEGIN)' which is a usage that
tripped me up in the first place.

Thanks for working on this!