When you edit any post other than the first post in a thread one of the options is "Move this post & any replies". Unfortunately the buttons in the post management table make it bigger than the rest of the tables on your page. Here is one way to fix it:
Open your ubbthreads/templates/default/editpost_manage_move.tmpl file and look for:
and replace that with:
</td><br /></tr><br /></table><br /><table border="0"><br /><tr><br /><td>
Now you'll have two rows of buttons, but only when you edit a post other than the first one in a thread (editing the first post in a thread will result in just a single row of buttons).