Hmmm. I'm on a mac, which has a property editor (...which doesn't help you).
I would make a copy of the properties file before you edit it just in case, and open it in wordpad instead and see if that works. In wordpad you might need to save it as type text document to preserve the formatting.
Maybe the editor is adding extra whitespace at the end of the file or something which you might have to remove?
(caveat emptor - all from memory when I last had a windows box about 2 years ago