It seems that the mediaproxy module depends on the domain module (mediaproxy uses the is_from_local() and is_uri_host_local() functions). I think this should be added to the "Dependencies" section of mediaproxy.
Interestingly, the mediaproxy works fine for me even without any actual data in the domain SQL table. I also don't see why the mediaproxy needs to know if a call is from local or not.... I'd appreciate if someone could enlighten me ;-)
Christian