As the title suggests, there’s at least one letter with a diaeresis that Plexamp has trouble displaying. I noticed this with the band Spın̈al Tap, who use the letter ‘n’ with two dots above it as their own spelling. German umlauts ä, ü, and ö, however, are displayed correctly. I can also confirm that ï is displayed correctly. I haven’t tested how it handles other letters (e.g., ÿ or ë). I don’t know if you can or want to fix this, but I thought I’d at least bring the issue to light.