MaxScale v2.1.2 Read Cache is not discarded after update/insert

We used the new cache filter of MaxScale with v2.1.2 in combination with thew readwritesplit and 3 servcers (but we also tested it with readconnroute and only 1 server with the same result).

We got an old script which updates a value in a mySQL table and afterwards it selects a sum where this value is used in a join. The result is that the sum still delivers the old value from the MaxScale cache. Afterwards, even when reloading the whole webpage with a fresh select, the statement is still outdated until the cache TTL is passed or until we restart MaxScale.

Shouldn't the cache data for this stable/query be discarded by MaxScale automatically after an update/insert?

Our cache config is:

[Cache]
type=filter
module=cache
hard_ttl=300
soft_ttl=290
max_resultset_size=512Ki
max_size=100Mi

the script causing this problem is a bit durty but easy to read:

...

    $conn = mysqli_connect($hostname, $username, $password, $database);
    $json = array('status' => 'false');
    $sql = "Select id from task_data where task_id =".$_REQUEST["task_id"]." and month =".$_REQUEST["month"]." and year = ".$_REQUEST["year"];
    $result = $conn->query($sql);
    if($result->num_rows > 0){
		$data_id = $result->fetch_assoc()["id"];
		$sql = "Update task_data set hours = ".$_REQUEST["hours"]." where id = ".$data_id;
		$result = $conn->query($sql);
		if($result){
			$json['status'] = 'true';	
		}
    }
	else{
		$sql = "Insert into task_data (task_id, month, year, hours) Values (".$_REQUEST["task_id"].", ".$_REQUEST["month"].", ".$_REQUEST["year"].", ".$_REQUEST["hours"].");";
		$result = $conn->query($sql);
		if($result){
			$json['status'] = 'true';	
		}
	}

	if($json["status"] == "true"){
		
		$task_hours = $conn->query("select ifnull(round(sum(hours),2), 0) as hours from project join task on (project.id = task.project_id) join task_data on (task_data.task_id = task.id) where month = ".$_REQUEST["month"]." and year = ".$_REQUEST['year']." and project.id = ".$_REQUEST["project_id"].";")->fetch_assoc()["hours"];
		
		$project_hours = $work_hours = $conn->query("select ifnull(round(sum(worked_hours),2), 0) as hours from project join day on (day.project_id = project.id) join data on(data.id = day.data_id) where month = ".$_REQUEST["month"]." and year = ".$_REQUEST['year']." and project.id = ".$_REQUEST["project_id"].";")->fetch_assoc()["hours"];
		
		$json["hours"] = $task_hours;
		$json["project_hours"] = $project_hours;
	}

...