Lately with Everett I've been having my exported audio files export without an extension on the end. It's fairly easy to just rename it and add a ".mp3" or ".wav" but it seems to be a new behavior I haven't seen before and I'm wondering if it needs to be reported.
 
This happens randomly. Sometimes it will work properly. Sometimes it won't.
AHA! I just figured it out. It will not save with an extension if there is a period "." in the name.
I've been saving songs with names like "4.5 This Song". It must think that since there's already a "." in the name it doesn't have to put an extension on it.

That period implies there's a suffix, which is expected to be format-specific.

I figured that was the case, however you can save project files with periods "." in them without any hitches.

There are all kinds of "special character" things that drive me nuts, especially when going back and forth with files between Windows and OS X...especially when backing up files made on both computers to a common disk. Argh!!