A SiteMap Question-- Bug?

[Jeevan]

We have a sitemap file( similar to below) with securitytrimming enabled in
the provider declaration. There is a menu that is bound to this sitemap.
<siteMapNode>

<siteMapNode url="~/Url.aspx" title="A URL" description="Some LinkA"
roles="rolea"/>

<siteMapNode url="" title="Group" description="Some Group"
roles="rolea,roleb">

<siteMapNode url="~/Url1.aspx" title="B URL" description="Some LinkB"
roles="rolea"/>

<siteMapNode url="~/Url2.aspx" title="C URL" description="Some LinkC"
roles="roleb"/>

</siteMapNode>

</siteMapNode>

When a user with roleb logs in he / she should see only the "Group Node" and
the " C URL" inside the "Group" Node, however it doesnt happen and "A URL"
still appears and so does "B URL".

While trying to figure it out we noticed that the roles on the sitemap seems
to work only at a Parent level .. Group in this example provided there is no
URL associated with it. Is this a bug? Any one come across this issue?



Thanks