I thought the same, but as it turns out you can't put an equal sign ( = ) in the value either. That's okay to put into XML. The only thing I can think of is that there is a parsing error with splitting on the =. I believe the same issue occurs if you put a name in without a value.
Actually you would want to use %3d for and equal sign. The name "query-string" implies "URL Encoding" not "HTML Encoding"