Underscores don't work in library hashtags

While attempting to set up my game using an MCC feature that allows you to populate your game with only your library sims with the hashtag #mccc_include, I found that any hashtag featuring an underscore will not show up when searched for.  However, removing the underscore allows search to find them.  It was my understanding that we could include underscores in hashtags, but they never show up when I do.