Selected page jumps being stripped

Hi, I have searched through the forums, but not found anything quite answering my problem. I have been implementing page jumps using this html code : http://en.support.wordpress.com/splitting-content/page-jumps/. I have been writing the code in the html tab and noticed that SOME but not all of the anchor html tags are later stripped from the page. I have been switching between the html and visual tabs (some people recommended staying in the html), but only some of the anchors seem to be affected. Where stripped, there is a &nbsp tag added. Replacing with
does not seem to change the behaviour. Where can I start looking to fix? Example page here: http://arcguiding.com/blog/activities/wildlife-guiding/. The behaviour does not seem to affect the first two anchors, but I can’t think why. Thanks in advance for any help.