That's because YouTube has done some mischief. Already Google is pushing its products into your face. Latest being, owning an account to comment on YT. I mean, WTF ?
So, here is the post describing the situation and an irritating discussion follows here in this google group but a good source for getting some help regarding downloading full 1080p videos can be found here
I know this is no permanent solution but I did a little bit digging and found out that 4kvideodownloader and youtubedownloaderhd seem to be working as of now(I personally confirmed it 2 days ago). However, it wouldn't be long before YT finds this out.