It might be best if I just post photos of what the thing is doing. I'll use the latest current build directly from the site; that's r25959. I can't understand why an older version would work better on a certain player than a newer version while other players remain unaffected.
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Okay, now I've loaded the latest version it is is working fine!

Weird. I'm going to update my source code and see if that will work, maybe I'll post a build with the problem just so you guys know I'm not going crazy (anyone with a 1g nano who'd like to try it?).
One problem I did notice however was very long delays (sometimes more than ten seconds) when seeking in musepack in later versions. When I copied code from the new musepack into 3.5.1 to see if I could play the sv8 musepack files, I also noticed the delays and thought I did something wrong. The old musepack code in 3.5.1 does not delay at all, seeking is immediate. The delay was noticed on a older musepack file that works in both versions so I can definitely see the difference.
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Now I have figured out how I got the letter glitch before. All I had to do was get rockdoom to crash between levels with a data abort and on the next boot the characters would either be screwed up or some words would use the wrong letters (one letter up). This happened with r25647, I don't know why everything is so inconsistent but one thing is certain: it makes testing very difficult.