This error has already been worked since version v1.0.8. Do the following. Create a new test instance (from scratch) with the latest RC version of Dgraph. (v1.0.10-rc1) - And try to Fetch this same error in this instance. If So see it persists tell us.
More details about your settings are also interesting to know.
Chek this commit:
https://github.com/dgraph-io/dgraph/commit/87790666d254f05e27f54c4647a0f8c869bbee59