The activation of the GZIP-Feature is not very intuitive. When its activated, I assume that all possible requests will be compressed. On the server side, the behavior seems ok, but on the client side the request aren't compressed. After some investigation, it looks like the change 1404700 introduced the "force" variable in the class GZIPOutInterceptor, which is not initialized. As its an boolean, per default its "false", and so the requests are not compressed.
Its not a bug. Please update the documentation or initialize the variable to make the behavior more intuitive.