See this KB article:
Incorrect font is applied after a style is applied to a form field in Word
2007 or in Word 2003
http://support.microsoft.com/kb/828501/en-us

Signature
Stefan Blom
Microsoft Word MVP
>I have a protected Word documetn that I am trying to control the font size
> in. I unprotect it and change the font size for the text area to 10.
> It's
> fine until I protect it again. Once protected, it will only enter the
> text
> at size 12. This distorts the page.