[need help] EWW / shr do not honor different font sizes

[physiculus]

hello,
i'm struggeling with html messages in gnus, as far as i understood, gnus
use shr to render html (the default set).
my first attempt to view a html message results in setting
some variables: shr-use-fonts and shr-use-colors both to t.
after that, words in html renders in colored, bold, italic. Great.
BUT
different font sizes are ignored.

here is an example:
Ein, zwei W¶rter in unterschiedlichen <font size="-2">Gr¶Ÿen</font>
      <font size="+2">Gr¶Ÿen</font> <font size="+3">Gr¶Ÿen<br>

if i view this mail with K H inside gnus, then the font sizes are
honored (only with external browser!).
therefore i think, it is a problem or a wrong configuration option
inside shr.

Any ideas?

Regards
Poul