Trying to redirect an upstream git:// url to a local git://xxx;protocol=file url doesn't work as there is no way to specify this in the mirror syntax.
Fixed in master with the fetcher patches before: http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=fa7c2b074354b0f1ec2614b2f339b7d3bf08c7e7