Why do indented explicit line continuations not allow comments in Python?

I'm writing a Python parser to learn Flex and Bison, and I'm trying to find out why only the first of these programs is valid Python.

a.py:

\# This is valid Python

produces no error.

b.py:

    \# This is not valid Python

produces this error:

  File "b.py", line 1    \    ^IndentationError: unexpected indent

and c.py:

if True:    pass    \    # This is not valid Python

produces this error:

  File "c.py", line 4    # This is not valid Python                             ^SyntaxError: invalid syntax

I'm using Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 (Ubuntu 10.04); However, testing on ideone.com suggests the behavior is the same on Python 3.

_{See also: How can I do a line break (line continuation) in Python (split up a long line of source code)?}