Dear @Marci,
Well, this is a bit inconsistent I must admit. When in 'gated' mode, the Gate and Selector actors do not give the upstream actors and "attention," i.e. values are not pulled from them. And it does look like the Movie Player stops, given that the indicator at the bottom stops moving. But, the background process of playing the movie is in fact unaffected. That's kind of a separate thing, and it unaffected when you "block" the actor using a Gate or Selector. (This is also the way it was in Isadora 1.x, so it's not a new behavior.)
As
@dbini said, if you really want the movie to pause, you'll have to send a speed of 0 in addition to using the Selector actor.
Best Wishes,
Mark