Immediately after leaving Hoth, Luke suddenly steers his X-Wing off course, and this exchange occurs:
INT. LUKE'S X-WING - COCKPIT
Luke, looking thoughtful, suddenly makes a decision. He flips several switches. The stars shift as he takes his fighter into a steep turn. The X-wing banks sharply and flies away in a new direction.
The monitor screen on Luke's control panel prints out a question from the concerned Artoo.
LUKE (into comlink) There's nothing wrong, Artoo. I'm just setting a new course.
Artoo beeps once again.
LUKE (into comlink) We're not going to regroup with the others.
Artoo begins a protest, whistling an unbelieving, "What?!"
Luke reads Artoo's exclamation on his control panel.
LUKE (into comlink) We're going to the Dagobah system.
Luke checks his readouts and makes a few adjustments. He rides along with only the soft hum of the instruments to break the silence. Finally, Artoo chirps up.
LUKE (into comlink) Yes, Artoo?
Artoo utters a soft, carefully phrased stream of whistles.
LUKE (into comlink, chuckling) That's all right. I'd like to keep it on manual control for a while.
I've seen this movie and this scene dozens of times, but a few days ago I was watching it and suddenly realized that it seems like Luke catches R2D2 trying to trick him. The script seems to confirm this.
Here's the way I see it now: R2-D2 REALLY wants to go to the rendezvous and continue fighting for the rebellion. He is horrified when Luke tells him that is not what they are going to do. R2-D2 thinks about this for a while, then offers to take over flying the ship for Luke. R2-D2 is hoping that Luke will agree to this, and that R2 can secretly redirect the ship to the rendezvous while Luke is sleeping or simply isn't paying attention. Luke sees through the clever ruse and "chuckles", then says "That's all right. I'd like to keep it on manual control for a while". He chuckles and refuses to hand the controls over to R2 because he knows that if he lets R2 take over, the ship will end up at the rendezvous, not Dagobah.
Am I the only one who thinks this is what is going on?