Board Thread:The Panopticon/@comment-4028641-20140106233604/@comment-25041817-20150908140715

Also, the Master did go back and change time, he just did it without actually traveling in time; too wit, he plants a bomb device in Bob Dovie's head that causes the TARDIS to be erased from time, trapping the Doctor on Gallifrey and undoing what he done after he left.

When the First Doctor deactivates the warning lights that caused the Doctors to fall into the trap, they pause for a moment and then go about their business, with, aside from a brief trip to Dovie's house, no evidence that the events of the day are recalled by any of them.