I guess because No Label
I installed the plug in and it works only in admin area when creating a new category.
Since this plugin attaches itself to textarea label I guess this is the problem. In the default theme texarea has no labels. this may explain why it works in admin but not on public pages.
I will have to fish for text area to see how it's constructed and maybe add a lable to it.
I tried all the other fixes but it didn't work for me. I really like this plugin. much cleaner than the alternatives.