[Power BI AP] POST Dataset relationship generates blank on filter

I have a dataset schema that looks like this 

{  
   "name":"sample",
   "defaultMode":"Push",
   "tables":[  
      {  
         "name":"Table1",
         "columns":[  
            {  
               "name":"date",
               "dataType":"DateTime"
            },
            {  
               "name":"Hour",
               "dataType":"DateTime"
            },
            {  
               "name":"Zone",
               "dataType":"string"
            },
            {  
               "name":"Type",
               "dataType":"string"
            },
            {  
               "name":"Price",
               "dataType":"Int64"
            }
         ]
      },
      {  
         "name":"zone",
         "columns":[  
            {  
               "name":"zone",
               "dataType":"string"
            }
         ]
      }
   ],
   "relationships":[  
      {  
         "name":"123",
         "fromTable":"zone",
         "fromColumn":"zone",
         "toTable":"table1",
         "toColumn":"Zone",
         "crossFilteringBehavior":"OneDirection"
      }
   ]
}

When I post the dataset, and fill it with rows, containing only two zones each. I get a blank in the filter viz. I don't have any idea where this blank comes from. Do you have any idea where this might come from ?