Is this intentional?
To prevent that from happening would require the voting system to test to see if the author and the person voting had the same account.
Is there a reason an author would not vote their own story a 10?
I can see two reasons. The first might be that after the story has been up a while the author reads it and decides to give it a vote based on how they would rate a similar story written by someone else.
The second would be to see the effect a single vote of a particular number might have on the overall score.
Looking at the number of votes for your stories, my guess is that the difference would be less than a tenth of a point for any of them.
Since the lowest and highest 10% of the votes are discarded, it might even be possible that a one vote in a story might actually increase the displayed score.