I am running dasBlog v.2.1.8102.813. I found when I tried to add comments that the Live Comment Preview didn't display the last allowable HTML comment tag. These tags are selected in the Configuration section under "HTML in Comments". With some help from the dasBlog forum on CodePlex it was determined that there was a bug in the LiveCommentPreview.js file.

In order to fix this bug, replace this line (line 60 in my file)...

if(tagNamesRegex.length > 0)
{
  tagNamesRegex
= tagNamesRegex.substring(0, tagNamesRegex.length - 2); } 

...with this line...

if(tagNamesRegex.length > 0)
{
   tagNamesRegex
= tagNamesRegex.substring(0, tagNamesRegex.length - 1); } 

Happy debugging!