Continuity mistake: In "The Deadly Assassin" the Doctor's blood is red but in "State of Decay" his blood is suddenly dark blue. Then it's back to being red in "The Two Doctors."
Continuity mistake: The Doctor somehow manages to secure his scarf across the catwalk, despite having only gone on seconds before the Master. He then manages to put it on again during the seconds it takes for the Master to alter the angle.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★