It appears to be mostly Warner titles purchased through Vudu...the bonus features bundled in are Ultraviolet enabled, but my UV account sees each bonus feature as a separate movie. For example, if you buy The Lego Movie with 10 bonus features bundled in, you'll check your UV account and discover...
I've noticed that when I buy a movie from Vudu with bonus features, sometimes each individual bonus feature shows up as a separate movie in my Ultraviolet account. This is very annoying.