Thanks for that tip about the serial buffer!

I was already sure it wasn't a serial buffer problem because my code handles single characters in and out in a fast loop, and my repro was only on that one U2 song going back and forth across it. But that tip is really useful and I will keep that in mind just in case I need it later.

I have traced it down to memory overwrite problems in the Arduino program's string handling which surrounds the processing of of track metadata. To make the bug go away, I can either skip the UTF-8 conversion step, or I can skip the logging that says "Artist changed to xxxx", either way the bug disappears. So it's some sort of bug related to the way those strings are handled. I'm going to poke at it some more and get the code updated to fix the bug.

Thanks!