There were about a dozen issues uncovered using this technique. I would say the majority of them were what I would call "real" bugs, as opposed to "sure, that doesn't work but nobody cares". One example is that gmake allows $$ in variable names, as in "FOO$$BAR=abc"; at the time our parser did not handle this correctly. I did not have to create special cases to fix these bugs, at least not any more so than any other parser feature.
