While recursively traversing a source directory, if a directory was encountered containing either no .coffee files (ex. an .svn metadata directory) or where the last file processed in that directory was not a .coffee file, compileJoin() might never be called.
This issue was originally introduced by a (well-needed) optimization in commit dc272a680b.
In join mode, anytime the 'unprocessed' count is decremented, the remaining file count should be evaluated to determine if it is time to run compileJoin(). Previously, compileJoin() would only ever be called in one of the four possible terminating branches of this recursive asynchronous operation.
Jeremy Ashkenas