Bingowings said:

When Luke comes back and Leia is missing Han orders them to stay put while he, the remainder of the command staff and two brightly coloured, reflective noisy machines go off to be captured for plot reasons.

Yup, Han flips a switch and that part of the film just turns off until he gets back. They weren't supposed to be captured, so the rebel troops wouldn't have expected them to be gone for so long....and were they supposed to attack the shield generator that day? Or was the plan to wait till the next day all along? The story structure really falls apart (again) as soon as they're captured by the Ewoks.