Running QCad Professional 18.104.22.168, on Ubuntu Linux 9.04 Jaunty Jackalope.
After upgrading to Ubuntu 9.04, I had problems with the object selection (small crosshair) pointer and the zoom pointer. Either or both were partially displayed, displayed in light gray, or not displayed at all. The symptom would change from file to file and session to session.
At first, I thought removing the version of QCad available in the Ubuntu repositories (which I don't think was installed until I upgraded to 9.04) might solve the problem. It didn't.
Checking in this forum, the post from Justine on 3 March 2009 looked promising. Anrew's response to try resetting QCad as described in FAQ 7, worked for me.