Npgsql.PostgresException (0x80004005): XX000: cache lookup failed for type 207852 when schema dropped

I', runining my test suite and try to use enums:

CREATE TYPE dockind AS ENUM ('I', 'O', 'Q');
CREATE TABLE document (
    doc_id       SERIAL,
    doc_kind     dockind NOT NULL DEFAULT 'O',
)

let openConn() =
    let conStr = localConnectionString()
    let conn = new NpgsqlConnection(conStr)
    conn.Open()


    conn :> IDbConnection
//Called after the schema is created
let initDb (conn:IDbConnection) =
    let db = conn :?> NpgsqlConnection
    db.TypeMapper.MapEnum<DocKind>("dockind") |> ignore

However, I'm getting a odd error:

Npgsql.PostgresException (0x80004005): XX000: cache lookup failed for type 207852
   at Npgsql.NpgsqlConnector.<>c__DisplayClass161_0.<<ReadMessage>g__ReadMessageLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlConnector.<>c__DisplayClass161_0.<<ReadMessage>g__ReadMessageLong|0>d.MoveNext() in C:\projects\npgsql\src\Npgsql\NpgsqlConnector.cs:line 1032
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming) in C:\projects\npgsql\src\Npgsql\NpgsqlDataReader.cs:line 444
   at Npgsql.NpgsqlDataReader.NextResult() in C:\projects\npgsql\src\Npgsql\NpgsqlDataReader.cs:line 332
   at Npgsql.NpgsqlCommand.ExecuteDbDataReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken) in C:\projects\npgsql\src\Npgsql\NpgsqlCommand.cs:line 1221
   at Npgsql.NpgsqlCommand.ExecuteScalar(Boolean async, CancellationToken cancellationToken) in C:\projects\npgsql\src\Npgsql\NpgsqlCommand.cs:line 1086
   at Npgsql.NpgsqlCommand.ExecuteScalar() in C:\projects\npgsql\src\Npgsql\NpgsqlCommand.cs:line 1063
   at CoreLib.Db.queryScalar[a,b](a con, String sql, IEnumerable`1 parameters) in /Users/mamcx/Proyectos/BestSellerPOS/CoreLib/DbStore.fs:line 184

Npgsql version 4.0.0

This happened when I drop the schema and rebuild it. If I don't rebuild this, it work. So how workaround this?

let createDb() =
    use con = openConn()
    let sql = openDbFile()
    exeSql con sql |> ignore

let testDb() =
    DbServer.createDb()
    let db = DbServer.openConn()
    DbServer.initDb(db)

I'm not using the reusing the connection for build the db and execute the tests.

Npgsql caches all the PostgreSQL types in a given database when it first connects to it (the types are cached on the connection string). If you make any changes to types such as defining a new one or dropping one, you must tell Npgsql to flush the type cache by calling NpgsqlConnection.ReloadTypes().