Sending synced/master to a bare git remote is unnecessary because master can be pushed directly to it.
This would be good to avoid, because the existence of synced branches can complicate situations such as a force push of master that discards commits from the tip of the branch. In that case, the user needs to worry about cleaning up the synced/master branches, on remote and the remote tracking branches, and the local synced/master branch, to avoid them getting merged back in.
Ideally the local synced/master branch should only exist when there are un-merged changes that have been pushed from another repository in distributed mode. Once those are merged, it should be deleted. And a bare repository should never have a synced/master branch.
(synced/git-annex is another matter, and is fine as it is) --Joey