I recently bought a new Android Phone with KitKat. This is the first time I'm using Android for more than simple phone calls and the occasional route planning. It's a quite decent OS.
However, one thing that happened to me was a usability nightmare. I use the phone to listen to music. So I uploaded a few albums, and some of them had the album art in the same place as the audio files.
The Google Gallery app is too smart for it's own good: it finds the album art, thinks it should manage the images, they get into the automatic upload/backup rotation, yadda. One suggestion I found was to use a .nomedia file inside my Music directory.
So I created a .nomedia file inside the Music directory. Great, no more album art in my gallery. However, the songs had disappeared as well from the Google Play Music library. The .nomedia is apparently to powerful, which isn't really surprising considering it's not called .nopics.
Well, no problem, I'll just delete the file, right?
Nope, removing the .nomedia file isn't good enough. Whatever I tried, the player couldn't find my audio files any more. Something in KitKat remembered that there was a .nomedia file and decides that seeing it once is good enough. The system never forgets the file existed, the information must be cached somewhere, and Android never bothers to check again if the file is still there.
Ok, this can't be such a big problem, there must certainly be a way to re-scan the drive? Yes, there is, it is possible to reindex the Music folder. However, on KitKat at least most scanning apps will just crash without any useful feedback. Apparently there were some changes in this release that are incompatible with older apps. The app that finally did work for me is SD Scanner.
If you found this post through a search engine, try SD Scanner if you use KitKat. If you don't, search for a scanning app that's compatible with your Android release. Good luck.