When I execute a search on the http://www.kdenlive.org web site it complains "You must include at least one positive keyword with 3 characters or more." - no matter what search terms I use.

Which word do you use for searching?

Like I said - any word gives the same result - but for eg "opengl". Does it work for you?

Is it my firefox browswer ? I have Firefox 17.0.

Nope ! same result on Google chrome