Anomalous behaviour when compiling regular expressions?

[Guest]

import reTraceback (most recent call last):
File "<stdin>", line 1, in ?
File "c:\python24\lib\sre.py", line 180, in compile
return _compile(pattern, flags)
File "c:\python24\lib\sre.py", line 227, in _compile
raise error, v # invalid expression
sre_constants.error: nothing to repeat

but
''

Why is there a difference in behaviour between the two cases. Surely the
two cases are equivalent to:
''

and
''

Harvey