Flock blogging interface provides an area for tags. However that's not useful for WordPress users if tagging plugin such as UTW is used. You'll have to double edit your post by logging into your blog normally to get rid of the tags inserted by Flock.
The workaround appears to be using embedded tagging, e.g. [tag]flock[/tag], will be a tag since they are wrapped. Let's see if this works.
PS: it doesn't work that way as you can see a "link to tag" is provided but no tag was inserted into the UTW tag list.