Branded Master-Pages

Hi,

I like to brand the master page an get each time the error:

http://localhost:81/_themes/20/test-18F500C1.css?ctag=21 404 (NOT FOUND) 

i´m loadeing the test.css in the master page with this code:

<SharePoint:CssRegistration name="<% $SPUrl:~SiteCollection/Style Library/bootstrap/styles/test.css %>" After="corev4.css" EnableCssTheming="true" runat="server"/>

when the attrs.  After="corev4.css" EnableCssTheming="true" removed, the css loads and styles the page.

i think the problem is that the theme engien doesnt copy the css to the _theme folder if i activate a theme,  something like... some ideas?