Bug?: <tspan ... dy ... text-decoration>

Hi *,

for me it seems the text-decoration within the tspan-tag does not work using
dy.

See this example:
*********************************************************************
<?xml version="1.0" encoding="iso-8859-1"?>
<svg>
    <text x="100" y="100" text-decoration="underline" font-size="20" >
        within the text-tag the text-decoration-tag works
        <tspan dy="40" x="100" text-decoration="underline">
            within the tspan-tag the text-decoration-tag fails
        </tspan>
    </text>
</svg>
*********************************************************************

I am using "Adobe SVG Viewer 3.0"

Any ideas?

thx in advance

PS: If this topic is already discussed, I beg pardon but the search engine
shows an HTTP error and I have searched not all by feet.