Can't get menus created with spumux to look good

I have some major problems to get menus created with spumux look good.

I have a highlight image with three colors + transparency. The image 
mainly consists of four ellipses. (See 
http://forum.videohelp.com/threads/325914-Spumux-problem)
The configuration file looks like this:

<subpictures>
<stream>
<spu
        force="yes"
        start="00:00:00.00"
        highlight="./menu/highlight.png"
 >
<button name="b1" x0="180" y0="020" x1="580" y1="148" up="bn" down="b2" 
left="bn" right="b2" />
<button name="b2" x0="180" y0="152" x1="580" y1="288" up="b1" down="b3" 
left="b1" right="b3" />
<button name="b3" x0="180" y0="292" x1="580" y1="418" up="b2" down="b4" 
left="b2" right="b4" />
<button name="b4" x0="180" y0="422" x1="580" y1="548" up="b3" down="bn" 
left="b3" right="bn" />
<button name="bn" x0="582" y0="450" x1="680" y1="550" up="b4" down="b1" 
left="b4" right="b1" />
</spu>
</stream>
</subpictures>

Everything seems to work fine, but the resulting menu is not good at all:
* The ellipses are in the wrong color, except in a few places where they 
seem to intersect with other ellipses (which are not visible except 
where they intersect).
* Some of the edges becomes light blue and some becomes dark gray. 
(http://forum.videohelp.com/threads/325914-Spumux-problem)

If I change the image to use only one color + transparency, then only my 
second problem remains.
I have also tried to specify "image"- and "select"-images in case they 
are required, but it doesn't make any difference.

What am I doing wrong here? I have searched for solutions, but noone 
else seems to experience the same problems.

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