Add this filter to the query.
Due to the nature of fapi, the value and the operator have an unintended level of indirection. You will find them in $this->operator and $this->value respectively.
Overrides InOperator::query
public function query() {
// Because this handler thinks it's an argument for a field on the {node}
// table, we need to make sure {tracker_user} is JOINed and use its alias
// for the WHERE clause.
$tracker_user_alias = $this->query
->ensure_table('tracker_user');
$this->query
->addWhere(0, "{$tracker_user_alias}.uid", $this->value);
}