ludusnaturae on "Changing font-family in MistyLook: size problems"

Every time I make a change of font-family in MistyLook (in two blogs), the font size changes by itself from a day to another. I get tired of fixing it and changing it every time I see the posts.
Seems it's not a good theme for these jokes. I'm dissapointed, because it's a theme I like and I'm using it in two blogs.
Seems I must give up and don't change the font-family anymore, or migrate to another theme ...
Is there Any way to fix this? Or am I doing something wrong?
I'm using the % tag for changing font size, but without any tag, size also changes.
Using Firefox, on Ubuntu and on Window$.