regexp weirdness (bug?)

[Sergey Schetinin]

Here's the session log:

>>> _re_pair="(?(plus).|-)"
>>> _re1=("(?P<plus>\+)"+_re_pair)
>>> _re2=("((?P<plus>\+))"+_re_pair)
>>> _re3=("(?:(?P<plus>\+))"+_re_pair)
>>> _re4="(%s)"%_re3
>>> import re
>>> print [re.match(_re, "+a") and 'match' for _re in [_re1, _re2,
_re3, _re4]]
['match', None, 'match', None]

this is not the supposed behaivour. all theese patterns should match,
right?