After changeset 1ef63e53714e MetadataWorkspace complains about SSpace space already being registered in some of the performance tests. Arthur suggested this might be a threading issue. The exception we are getting looks like follows:

System.InvalidOperationException: The ItemCollection for the 'SSpace' space has already been registered.
at System.Data.Entity.Core.Metadata.Edm.MetadataWorkspace.RegisterItemCollection(ItemCollection collection)
at System.Data.Entity.Core.Objects.ObjectContext.EnsureMetadata()
at System.Data.Entity.Core.Objects.EntitySqlQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery.ToTraceString()
at ...