This seems related to http://bugs.python.org/issue1218234 as well. 
This is my first bug report. I hope I do this right.
I posted this to comp.lang.python and was directed here. Here is a
chopped paste of that post:

I am getting an error on line 510 of inspect.py:

504    if iscode(object):
505        if not hasattr(object, 'co_firstlineno'):
506            raise IOError('could not find function definition')
507        lnum = object.co_firstlineno - 1
508        pat = re.compile(r'^(\s*def\s)|(.*(?<!\w)lambda(:|\s))|^(\s*@)')
509        while lnum > 0:
510            if pat.match(lines[lnum]): break
511            lnum = lnum - 1
512        return lines, lnum

I finally figured out that there was a caching problem. The function I
passed was changed, but the code lines (strings) retrieved by
linecache.getlines() (on lines 464 and 466) didn't update with the new
module contents... To get around this, I invoke linecache.clearcache()...

    linecache.clearcache()
    lines, n = inspect.getsourcelines(fn)


While inspect uses the cached module to get the text, the line number
used to find the block of source lines is retrieved from the passed
object. So, if I pass a function which reports that it starts on line
50, but in the cache it starts on line 40, an error isn't raised but the
lines of code returned are wrong. The error only occurs when the line
number is higher than the number of lines in the cached module.

Cheers,

- Rafe