Fix for issue #132

Added tests and fixes for use-cases found in my code and in existing tests.
I'm pretty sure that some cases not covered by this fix.

BTW: I've added thread culture reset to invariant culture for TestBase nunit fixture, cause I have a lot of failing tests due to errors parsing numbers with fraction part separator ("," vs "."). I didn't research it, but assuming I have no problems with it in production code, this must be only issue with tests.