Negative values for borrowedReservesCount in User schema

There are occurrences of negative values for borrowedReservesCount field in the User schema.

To Reproduce
On the playground https://thegraph.com/hosted-service/subgraph/aave/protocol-v2?version=current the borrowedReservesCount can be a negative value.

{
  users (where: {borrowedReservesCount_lt:0}) {
    id
		borrowedReservesCount
    reserves {
      reserve {
        name
      }
      currentTotalDebt
      currentATokenBalance
    }
  }
}

Expected behavior
The borrowedReservesCount should be always >=0. I assumed that a negative value meant that no reserves have been used for borrowing, however by querying

{
  users (where: {borrowedReservesCount_lt:0}) {
    id
		borrowedReservesCount
    reserves (where: {currentTotalDebt_gt:0}) {
      reserve {
        name
      }
      currentTotalDebt
      currentATokenBalance
    }
  }
}

you can see that there are reserves with non zero debt (e.g.

 {
        "id": "0x0360414fa5e5846f687096c82e1434151743e886",
        "borrowedReservesCount": -1,
        "reserves": [
          {
            "reserve": {
              "name": "USD Coin"
            },
            "currentTotalDebt": "488152768",
            "currentATokenBalance": "0"
          }
        ]
      }

Start with the User schema and the code that updates borrowedReservesCount, then reproduce the two GraphQL queries from the issue against the Aave protocol-v2 subgraph. Trace the example user with nonzero currentTotalDebt and determine why the count becomes negative; done means the count remains >= 0 while matching the user's borrowed reserves.