When you look in the "Finances" box on Manage My Team, for your last attendence, the % full is based on your current arena size, not the arena size as of the date the last game was played. So if you complete an expansion, the % full for the "Last home game" will be too low, as it will be calculating the pre-expansion number of tickets sold divided by the post-expansion number of seats.
Pretty minor, and should "fix itself" within a week, but still not what I would expect to see when I look at that piece of information.