Question about face on text with variable heights

[MJ]

I have some text mixed with characters of variable height on the same
line. They could be using different fonts (with :height text property)
or have display property with image and thus the line will appear taller
than others, which is obvious and okay.

When smaller text is specified with some text properties such as
:background, :underline or :box, they are drawn as tall as the tallest
text on the same line. For example, if I put :box on a word of 10 pixels
while there is other text of 36 pixels, the box will be as high as 36
pixels. I'd expect the box will be only 10 pixels. For :background color
and underline, it's a similar issue. 

Is this what Emacs (v22) is supposed to do? Is there a way to work
around this?

Thanks.
-- 
MJ