Revealing mistake: After the battle between Obi-Wan and Anakin/Darth Vader, Vader lies badly burned on the ground slowly crawling up. Palpatine's shuttle flies by, as seen by a shadow. However, even the lava in the shadow turns dark, like the lava is glowing from an external light source instead of glowing within itself. (00:57:50)
Revealing mistake: When Grievous and Obi-wan are fighting, as Grievous hits Obi-wan making him fly through the air hitting his vessel, it is quite obvious it is a stunt double instead of Ewan McGregor. (01:03:45)
Revealing mistake: When Yoda knocks Darth Sidious backwards over his chair, you can see the stuntman's hand. Sidious's hands are old and his nails are dark around the cuticles, but the hand during the flip is perfectly healthy and a different size. (01:45:35)
Revealing mistake: When Anakin dropkicks Obi-Wan on the table you can see, even without slow motion, that his feet aren't near him at all. (01:46:35)
Revealing mistake: When Anakin and Obi-Wan use the force to throw each other through the air, as Anakin lands on the panel, the stunt double is quite obvious. (01:47:35)
Revealing mistake: When Anakin and Obi-Wan are fighting on top of the table, after Anakin kicks Obi-Wan, we see a wide shot of Obi-Wan hitting the table, followed by a close-up of Anakin charging at him. You can see that the one who comes toward him is not Hayden Christensen, but his stunt double. (01:51:15)
Revealing mistake: When Anakin and Obi-Wan are fighting on the big table, in the wide shot where Obi-Wan kicks Anakin for the second time, you can see that the one who performs the kick is not Ewan McGregor, but his stunt double. When Anakin lands on the table in the next shot, the one left standing is also McGregor's stunt double, and this time he is even wearing a brown bandanna that Obi-Wan does not wear. (01:51:15)
Revealing mistake: Computer generated characters that have light sabers (like Yoda) show a glow on them from their sabers when they are on. All "live action" Jedi do not.
Chosen answer: Powerful force users seem to have some degree of control over their bodies even after death. In the later series, Luke's wife Mara Jade Skywalker only allows her body to disappear when her killer, and nephew Jacen Solo arrives at her funeral as a clue. Thus it appears that a powerful force user can simply choose if they wish their body to disappear.
Darius Angel