I mean sure, they had the same problems...sorta... during the filming of ESB. Mark Hamill was concerned on how he came off in the scene and everyone else was worried about the snake not moving or the smoke machine not working. But at least they came back to Mark to see how his acting held up. In the PT, they just swept it under the rug and it shows.
Acting is about pretending but is about becoming a new character. It's not so much about "make-believe" and imagination. I pretended all the time. I imagine myself as a hero on an amazing journey, but I'm just playing around in the back yard. You put me in a blank green room and my acting skills suddenly suck and my reaction to that evil lord (the tree in the back yard) is really lame.
You can't become a good character and react to something that isn't there. You can see that in TPM too. You've got Ewan looking at something just above Jar Jar's head, but not exactly looking at him. Or most of the time they are looking in Jar Jar's direction, but they are looking THROUGH him, not AT him.