[Plugin: WordPress SEO by Yoast] double title

hi

i just installed WordPress SEO and now my page title appears twice,
like this:
<title>about me about me</title>

in the snippet preview it looks fine. (it appears once)

it happens both if i fill the SEO title or if i leave it empty

how do i fix it?

thanks

lenny

http://ww.wp.xz.cn/extend/plugins/wordpress-seo/