While working on a test case for Format Paragraph (http://bugs.python.org/issue18226) I noted that format paragraph doesn't work with comment blocks when a comment block is selected.  The fix is very simple by changing one line:
if first and last:
    data = text.get(first, last)
    comment_header = get_comment_header(data)
else:

The comment_header line was changed from comment_header = ''.  This forces the format paragraph extension to always do "just a normal text format".  Attached is a patch but I would like to explore the bug in more detail and make sure all cases are covered.

I expect to find things like this while writing tests. A small fix can be part of the test file commit, like I did with configSectionNameDialog and its test. In any case, where is the test that fails without the patch and passes with it? It should be part of this patch, whether it is included with the test patch or kept separate.

Terry,
   I was suffering from the classic chicken and egg problem so I was not sure if the test case in http://bugs.python.org/issue18226 should include the small code change.  I will work with Phil Webster to get this small change added to issue 18226 along with test cases.  Thanks!

New changeset 841984e96df6 by Terry Jan Reedy in branch '2.7':
Issue #18429: Add user-oriented News entry about Format / Format Paragraph
http://hg.python.org/cpython/rev/841984e96df6

New changeset 9eea6401b892 by Terry Jan Reedy in branch '3.3':
Issue #18429: Add user-oriented News entry about Format / Format Paragraph
http://hg.python.org/cpython/rev/9eea6401b892

The 'fix', including the test, is included with the patch for #18226.  It shares with normal text the problem that selections of partial lines do not work well. I think this might be fixed in #18583 by only re-wrapping complete lines.