
Continuity mistake: On Utapau, when Obi-Wan faces off with Grievous, Grievous sends 4 MagnaGuards against Obi-Wan. Obi-Wan Force-pulls something from the ceiling to crush the droids. But in the ensuing fight between Obi-Wan and Grievous, the ceiling thing and crushed droids are gone.
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