Filter for subtype not working on Story added webhook

I have created a Webhook when a story gets added to tasks in a specific project; the goal of this webhook is to retrieve the old_section and new_section, which are part of the story added event.

However; the webhook is not only receiving the section changed stories, but all new stories in the project; including comment_added, custom_field_changed etc

This is the payload I use when creating the webhook:

{
  "data": {
  	"filters": [
      {
        "action": "added",
        "resource_subtype": "section_changed",
        "resource_type": "story"
      }
    ],
    "resource": "project gid",
    "target": "xxx"
	}
}

According to the webhook filter specs, this is supposed to work; as this is the raw webhook:

{
“events”:[
{
“user”: {
“gid”:“user_gid”,
“resource_type”:“user”
},
“created_at”:“timestamp”,
“action”:“added”,
“resource”:{
“gid”:“story_gid”,
“resource_type”:“story”,
"resource_subtype":“section_changed”},
“parent”:{
“gid”:“task_gid”,
“resource_type”:“task”,
“resource_subtype”:“default_task”
}
}]
}