The MP3 skips and pops are the same if in the internal or external and is mainly due to the low operational ram the device has.
The mapping is not a glitch. Internal was mapped as sdcard and external as media storage. This set-up would be GREAT if the sdcards were hotswappable, since no worry about apps crashing when pulling the card. Sadly, it is not, so no point in mapping the internal as the sdcard.