Why do my actors sink when I use a matinee?

So when I start up a matinee I go create new empty group, then create new movement track, then I add my actors to it. The problem is that once I add the actors and try to start moving them they lower themselves into the floor I have set up beneath them. They just move on their own. And If I have several actors at once then they all are in the same space as well… Any help with this issue would be greatly appreciated as I am just a student who is just learning how to do any of this.