At least since version 4.5.5 there is a bug with the highlighting of the icon in the Task Manager widget: the window may get the flag 'attention required' turned on but the flag is not dropped after the window gains focus. I use 'Focus follows mouse' (a.k.a. Sloppy focus) so the window may gain focus by entering it's display area with mouse cursor - without clicking. With this setting I can observe the problem not always but often (several times a day). Giving the focus to the window by clicking in it or it's icon usually clears the flag. Window with this flag are highlighted in the Task Manager widget (the widget typically placed on the main panel). I've modified my system to highlight the window's icon in Task Manager with red color (the original theme does not make it very distinct) and I'll attach a screenshot with a single Firefox window opened on the desktop that has focus (as shown by blue decoration of the window), but still with red icon on the taskbar. The feature is useful for example when a iconified window with IM conversation receives a new message. I suspect that there are more bugs related to handling of this flag because I often get the window's icon highlighted without an obvious reason, but I'm not able to pinpoint it. Reproducible: Sometimes Steps to Reproduce: I'm not sure how much it is related to the bug but it's the only thing that I can think of and may have influence: 1. System settings-> Window Behaviour -> tab Focus -> combobox Policy is set to "Focus Follows Mouse' Actual Results: The window's icon is displayed with 'requires attention' style even when the window has focus. Expected Results: When the window has focus or gains focus by any means, the 'requires attention' style should be cleared. I did have a look on Task Manager widget source code and as far as I could see it is only passing the 'requires attention' flag around, but the flag value is actually generated by kwin.
Created attachment 72376 [details] screenshot showing the bug Screenshot with only window on the desktop that has a focus and still shows on Task Manager with red icon - indicating that it requires attention.
When it happens next time, can you please use konsole to issue xprop | grep _NET_WM_STATE_DEMANDS_ATTENTION the cursor will turn into a cross, click the affected window (the click is not passed) and you'll get some output - or not. We'd need to know the result. Thanks.
That is going to be difficult because the screenshot where I show the bug was taken when I had one konsole window on one desktop and the FF window on another desktop. When switching desktops the highlighting of the FireFox icon was kept so I was able to start the ksnapshot from konsole, set it up to wait 2 seconds before taking the screenshot, switch the desktop to the one with the FF window and finally get the screenshot. I was considering to file the bug a long time ago but even acquiring a good screenshot was a problem. Opening a new window on the same desktop causes change of focus, and the symptoms are gone. Starting xprop on another desktop will disallow changing the desktop with mouse. I can try to switch the desktop with keyboard or try precede the xprop with sleep, but it can be quite difficult to get the desired result. But I promise to try.
sleep 10; xprop | grep _NET_WM_STATE_DEMANDS_ATTENTION
Created attachment 72431 [details] output of xprop for single FF window on desktop with highlighted icon The _NET_WM_STATE_DEMANDS_ATTENTION is not present in the xprop output :-( Does it mean that the icon in Task Manager is highlighted due some other reason rather than 'attention' flag?
There's ether a bug in the taskbar, or in libtaskbar, or: ... does this happen with anything but FF (or maybe Thunderbrid)?
It happens with all sorts of applications. Firefox, Eclipse, kopete, konsole, VirtualBox ....
Should be fixed with gd3b3cd4.
*** This bug has been marked as a duplicate of bug 275835 ***