DELETEing a YouTube watchLater playlist item failing - returning 404

i have code that deletes an item from my youtube watchLater playlist. this was working ok up to about two weeks ago - now i'm getting a 404 error from youtube.

here's the sequence of requests and responses (with authentication details stripped, of course):

get playlist items request:

GET https://www.googleapis.com/youtube/v3/playlistItems?fields=items/id&part=snippet&playlistId=WLlue5EIJLscoxMgEkEZfq_A

get playlist items response:

{
 "items": [
  {
   "id": "V0xsdWU1RUlKTHNjb3hNZ0VrRVpmcV9BLjU2QjQ0RjZEMTA1NTdDQzY="
  }
 ]
}

delete request:

DELETE https://www.googleapis.com/youtube/v3/playlistItems?id=V0xsdWU1RUlKTHNjb3hNZ0VrRVpmcV9BLjU2QjQ0RjZEMTA1NTdDQzY=

delete response:

{
 "error": {
  "errors": [
   {
    "domain": "youtube.playlistItem",
    "reason": "playlistItemNotFound",
    "message": "Playlist item not found.",
    "locationType": "parameter",
    "location": "id"
   }
  ],
  "code": 404,
  "message": "Playlist item not found."
 }
}

when i view the playlist via the youtube web site, i can see that the item hasn't been deleted.

the docs for the api indicate that i'm doing everything correctly. while debugging i noticed that the playlist item id is a base64 encoded string; i get 404 using both the encoded and decoded string.

this issue isn't limited to one particular item; it appears any item i place in my watchLater playlist cannot be deleted. i don't have any issues deleting items from other playlists; only watchLater is having this problem.

anyone have any idea what's going on?

Edit (Oct 2016): Google have said the Watch Later playlist has been deprecated. See https://developers.google.com/youtube/v3/revision_history