Update TypeChecker.fs

Author: dsyme

src/fsharp/TypeChecker.fs

@@ -14137,7 +14137,7 @@ module EstablishTypeDefinitionCores =
 
         let vis,_ = ComputeAccessAndCompPath envInitial None id.idRange vis parent
 
-        CheckForDuplicateModule env id.idText id.idRange
+        CheckForDuplicateModule envInitial id.idText id.idRange
         let id = ident (modName, id.idRange)
         CheckForDuplicateConcreteType envInitial id.idText im
         CheckNamespaceModuleOrTypeName cenv.g id