It looks like this problem popped up because of the introduction of the CatalogUrlFilter and ContentUrlFilter.
The filters access the parameter map before the code in the RequestHandler gets the opportunity to set the request's character encoding to UTF-8, once the parameters are parsed on first access setting the character encoding afterwards has no effect. Because these filters are mapped to all path requests they also affect the normal /control/ path, which wouldn't have had this issue prior to their introduction.
We need to find somewhere very early in the request handling to set character encoding to UTF-8. We can either add tomcat's SetCharacterEncodingFilter to all of the web.xml files or we can add similar code to the ContextFilter and ensure it is always the first filter to run.