The error basically says that the prepared statement is still active.

Why don't you always see this error? The key here is that your driver will automatically close the prepared statement for you after the entire result set is fetched. If the query returns a single row, your code will be fine, as after one fetchrow_array, the statement will be closed. In case the query returns multiple rows, this is where the problem is in introduced: as there are more rows left to be fetched, the statement stays active, and the error comes up when you disconnect.

To get all rows, either loop through the result set by calling fetchrow_array, or call fetchall_arrayref to return the entire result set.