In dual-screen (XInerama) configuration on single display with 2 screens create Task Manager Panel on each screen. In Task Manager Settings of each Panel check 'Only show tasks from the current screen', all other Filter should be Off. Then create some window -- open Konsole. Then move it from Screen 1 to Screen 2, you will see how entry from Panel 1 has been moved to Panel 2. Then maximize window -- you'll see that entry appeared again on Panel 1! Now it's on both panels, though window is only on Screen 2! Reproducible: Always
*** This bug has been marked as a duplicate of bug 268259 ***