The grouping of active windows in KDE task-manager has a serious bug in it. The bug works in the following way.

When you have a group of Firefox windows open and they are arranged by activity (or alphabetically) in the group. The trigger for the crash is when Facebook is open and a new message appears. This makes the window order being moved as the Facebook browser window blinks (notification of a new message) . This also results in the window being moved up and down as the header text changes. When attempting to click the active windows (in this case, Facebook) is difficult as it moves, after few attempts the task-manager crashes. Log-out is needed in order to restore the function of the task-manager.

I have not found any settings to change this behaviour in the task manager and I have been looking for it.

Reproducible: Sometimes

Steps to Reproduce:
1. Create open windows (Firefox or other browser) so that a group of open windows is created. 
2. Open Facebook and get a new message. This creates the active Facebook window to blink and move up and down in the window group. 
3. After several attempts to click the windows (difficult as it moves around when attempting to click) the task-manager crashes.

Actual Results:  
The task manager crashes and logout is needed to get it working again. 

Expected Results:  
The task manager should not move the window up and down and should not crash.

This bugs happen in KDE version 5.7.4 running on Gentoo Linux. The error message I get from dmesg is this one. No other error message appears.

"949747.031966] kactivitymanage[3601]: segfault at 7f400c01cc50 ip 00007f40001a4071 sp 00007fff66c2e8d8 error 4 in libQt5Sql.so.5.6.1[7f400018f000+42000]
[949747.122753] traps: ck-remove-direc[21748] trap int3 ip:7feff0ede537 sp:7ffcbaa39ce0 error:0
[949758.146407] traps: ck-remove-direc[21835] trap int3 ip:7f9770946537 sp:7ffd0de237c0 error:0