Text rendering issue, lowercase 'a' and 'o' too large

I’m having a very strange issue with text rendering. I have a dynamic text field that displays text from an external XML file.

The font is Arial size 12. When I set the Anti-alias bitmap (none) it displays as expected. But, when I set it to anti-alias for readability the lowercase ‘a’ and ‘o’ characters appear to be one size larger than the other characters. I have all upper and lawercase character embedded.

Just for kicks I moved the font size down to 11 and it appears normal. Also tried moving it up to 13 and appeared normal then too. So it’s only a problem with Arial size 12 with anti-alias for readability.

Any clues to this strange behavior? I really need to use that font size so just changing to another size is not a solution.