[A[_2_]]

I have Word 2007.

In creating numbered lists, I click the Numbering icon on the menu. Numbers
1 through 9 automatically puts maybe two spaces between the number and the
start of the text I type.

When it reaches 10 and beyond, the space between the number and the text has
more than tripled for some reason. In other words, like this:

9. Sentence starts here.
10. Sentence starts here.

What's going on and how do I fix it?

Thanks,
John