I just purchased Poweramp and am on beta-build-796-play. I noticed a really annoying bug. I often download music to my internal storage (music folder) and then copy those files to my music folder on my external SD card. It's just sometimes, the new tracks just flat out won't show up. I have triple-checked that those folders are ticked properly. Another curious case is I move the music to another subfolder in the same music folder, it suddenly recognizes the tracks, from there on I can again move the files over to the original location and it works fine most of the time.
Example for clarity - Let's say I downloaded a track to internal/music/artist/, then moved artist folder (yes the whole artist folder) to external/music/rock/ so that the tracks are in external/music/rock/artist. I start up Poweramp, scan library but the track doesn't appear. I then move the artist folder to external/music and voila, the track shows up like it should. Now I can move the folder back to external/music/rock/ and it will still work (most times at least).
I have tried some common things I could think of including Full Rescan but even that doesn't fix it. Weird.
Hope I can find some solution to this problem.
EDIT: I tested out various scenarios and this bug seems to occur when when the file is located in external SD card. Basically the first time you copy a file to your SD card the scanner doesn't see the file, but if you move the file around in the SD card then the scanner starts working as it should. Hope this helps
E2: Apparently you don't need to necessarily move the files actually, just renaming the files or containing folder does the job.