Yesterday I installed the LaTeX plugin for Kopete, but after a couple of restarts of Kopete I didn't manage it to work. The text remained unfiltered so I saw $$\sqrt(x)$$ all the time.

It seems I had an option enabled in the Kopete settings which disabled filtering of the text. After I disabled Settings->Configure->Appearance->Colors & Fonts->Do not show user specified rich text I could see the LaTeX output.