Other mistake: When Obi-Wan drops the block on the MagnaGuards, the one sticking out still has his photoreceptor on his chest. When Obi-Wan cuts his head off, he should still be able to move because he still has the photoreceptor. MagnaGuards were specifically designed to be able to fight without their heads. (00:57:53)
Other mistake: When Bail Organa jumps into his speeder after watching the young Padawan get killed, as the speeder starts moving, he turns the steering control to the left for a few moments, but the speeder still goes straight forwards. (01:21:40)
Other mistake: During the scene of Anakin's transformation into Darth Vader, there is a close up shot of his face just before his helmet is put in place. All of his face is shown as being badly burned with the exception of his eyelashes, which are still impossibly there. Subjecting one's face to any heat source hot enough to sear one's face will also burn away one's eyelashes as well. (02:01:25)
Other mistake: To escape from the elevator, Anakin cuts a hole in the ceiling. Later, when they rescue the Chancellor, they almost get crushed by another elevator (it is another one. Each elevator has a number. Obi Wan said the number of this elevator before and it was different than the one that had the hole). However, when a shot of this elevator is shown, it has the same hole that the other elevator has (better seen in slow motion).
Other mistake: In the final stages of the Obi-Wan/Anakin battle, they are fighting while floating over lava on a piece of metal. Just before Obi-Wan jumps to the high ground, we get a close-up shot of Obi-Wan (lightsaber pointing left off-screen) and then Anakin, (lightsaber pointing right off-screen) In this shot, Anakin's right hand is uncovered/real, and his left is gloved/mechanical, when it should be the opposite.
Answer: Darth Vader has a special chamber in which parts of the suit can be removed for comfort. When he is not in the chamber he must wear it at all times in order to survive.