Issue with filtering on tags and Windows Live Writer


I have an issue with Windows Live Writer (WLW) and tags. When publishing posts from WLW the post cannot be filtered using any of the attached tags.
I'm using Umbraco 4.7.2, with SQLServerCE 4. I've tried both blog4umbraco 2.0.26 and the Blog Startkit (which I assume is a version óf blog4umbraco?).
When a post has been published from WLW it all seems fine. The post is there and the tags are displayed. However, the post is not displayed when filtering on any used tag.
What I've got so far:
I'm very new to Umbraco so I don't really know how everything is connected. But in the database table cmsContentXML every(?) blog post is stored as XML, and the XML has an <tags>-element. When posting with WLW the <tags> only containts an empty CDATA. It seems like the BlogListPosts.xslt uses this tag to do the filtering.
If I just republish the WLW-posts (hitting the publish button), the <tags>-element is populated and the filtering works.
The XSLT-script also use "tagsLib:getTagsFromNode()" to get tags for each post, maybe this can be used when filtering?