Comment on WordPress SEO by SEO Dave.
If you add a Description to a Category you’ll see it as the title attribute for the Category link instead of the usual-
“View all posts filed under Category Name”
When you hover overthe link in a browser.
If you hover of this pages Categories (currently 2 Cats), one has the default View all posts…. and the other a slight derivative of the Categories name.
This is how it’s meant to look.
I wouldn’t worry much about what goes in your title attribute (not the same as the title element or title tag as a lot of people wrongly call it since Google etc… completely ignores it’s contents.
You see all these so called SEO experts adding keyword rich title attributes to their text links and even image links, but they didn’t go to the trouble of testing if Google actually counts it towards a pages SERPS (it doesn’t). See for test details.
Thinking about it, if you tried to add html code to the description that could cause a mess.