I recently sideloaded a couple Android apps (Kindle and 2 games). I went to play some music and noticed that there were two entries for each song. I used a file browser and saw that they were in the regular music folder as well as a music folder under Android.....?
I deleted the files in the Android music folder - went back to the music player and now they're all gone!
The Android folder is shown as 'Misc' and it just has mirror image of the files on your PlayBook. This is done because Android applications are designed to read the file structure in a particular format. If you delete file in any one place, it will be deleted in both. Try to stay away from files placed in Misc folder, as they are automatically positioned there and updated incase of any deletion.