When you have two lines of identical indentation, except that one uses spaces and the other uses tabs (eight spaces to a tabstop), then the tokenize module raises an IndentationError which coverage doesn't catch.
This can be considered a bug in the indentation, but it's only a style bug, as the code works just fine.
This could be considered a bug in tokenize, but I assume it's unlikely to get fixed.
It's a bit of a pain to fix in coverage, I think, because you're seeing it in the looping expression of a for loop. The loop would have to be restructured to pull the tokens from the generator inside the loop, inside a try/except, and either error out usefully (with filename and line number!) or try to go on. Still, it might not be too bad.
The attached file demonstrates the problem.