On a two-monitor configuration with the primary monitor on the right and the secondary on the left, after clicking on KMix tray icon on the primary monitor the pop-up appears on the secondary monitor. Reproducible: Always Steps to Reproduce: 1. Get yourself two monitors. 2. Configure them so that the primary one is on the right and the secondary one is on the left (see screenshot). 3. Also, activate "active window follows the mouse" in Window Behavior settings. 4. Click on the KMix icon in the tray. 5. Enjoy the long way your mouse will take to reach the pop-up.
EDIT: it should be "Active screen follows mouse" under Personal Settings -> Window Behavior -> Focus.
*** This bug has been marked as a duplicate of bug 333803 ***