I am having a rather perplexing bug. Whenever I close an application window, such as firefox or dolphin, knotify crashes. The following error occurs: The application KNotify (knotify4) crashed and caused signal 11 (SIGSEGV). Any ideas on the solution to this problem? 
Thanks in advance.
Bugs regarding similar problems (with knotify4) have been filed. You can for now turn off sound notifications in knotify4 (from personal settings -> notifications -> system notifications) for processes such as minimise, maximise, close window etc. (since the problem is with the sound part of knotify). This should reduce the crashes significantly. If you badly need the sound notifications you can try using external player like mplayer with knotify (personal settings -> Notifications -> System Notifications -> Player settings -> use an external player and enter: mplayer).