Hmmm.  This strikes me as a bug, beyond the realm of Issue 3262.  The
two items may be related, but the dropping of the 'a' seems like
unexpected behaviour that I doubt any current code is expecting to
occur.  Clearly, what is going on is that the Engine starts scanning at
the 'a', finds the Zero-Width match and, having found a match,
increments its pointer within the input string, thus skipping the 'a'
when it matches 'bc'.

If it is indeed a bug, I think this should be considered for inclusion
in Python 2.6 rather than being part of the new Engine Design in Issue
3626.  I think the solution would simply be to not increment the ptr
(which points to the input string) when findall / finditer encounters a
Zero-Width match.