Highlight search result does not work with span

I cannot highlight my search result when using span:{near:{…}}

I get an error like this

Reason: PlanExecutor error during aggregation :: caused by :: Remote error from mongot :: caused by :: Duplicate key text (attempted merging values $type:string/text and $type:string/text)

by typing this query

{
  index: "simple",
  span: {
    near: {
      clauses: [
        {
          term: {
            path: "text",
            query: "stöd"
          }
        },
        {
          term: {
            path: "text",
            query: "till"
          }
        },
        {
          term: {
            path: "text",
            query: "start"
          }
        }
      ],
      slop: 5,
      inOrder: false
    }
  },
  highlight:{path:'text'}
}

but if I remove the higlight-part my query returns the expected result:

{
  index: "simple",
  span: {
    near: {
      clauses: [
        {
          term: {
            path: "text",
            query: "stöd"
          }
        },
        {
          term: {
            path: "text",
            query: "till"
          }
        },
        {
          term: {
            path: "text",
            query: "start"
          }
        }
      ],
      slop: 5,
      inOrder: false
    }
  }
}

This is only an issue for span.

Please help me.