While looking through some JSPs, I noticed something:
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
I've highlighted the important parts. The web server is set to tell the browser that the page is encoded in UTF-8. The page itself, on the other hand, tells the browser it's ISO-8859-1.
Thankfully this had been fixed at some point, so you can tell which original file was used for the copy-paste depending on what the charset is in the <meta> element.
And I know it's my fault. Eclipse has it in its default JSP template and I never bothered removing it, so it got copy-pasted all over the place.