You can get a good feel of what's happening if you view the Now and Next view on your Empeg. Select all your tunes, shuffle them all, then play around with the tweak order buttons (or Popup menu).

The tweak is not recursive, it will not tweak ALL songs by the artist up next to the current one, it only works on the next song. If you press tweak order more than once it will stack the songs up next to the last one. Mess around with it in Now and Next, just so you get the feel of it.

Really the only way to undo the tweak is to re-load the playlist, but if you have shuffle on they won't be in the same order again. I think the intention was to just tweak a few songs then go back to the random playlist.