So, I encountered this both on Fedora that I tried and Open Suse which I'm trying now. In places including but not limited to dolophin's places sidebar, panel's add widget menu and desktop effects settings. The scroll step is less than one line and is not affected by changing scroll step in mouse settings, while this setting does affect scroll speed in for example web browser or even dolphin's main panel. Video included: https://www.youtube.com/watch?v=n2BDi_-AaH8 Problem was discussed also here but only related to dolphin: ttps://bugs.kde.org/show_bug.cgi?id=342839
*** This bug has been marked as a duplicate of bug 355410 ***