Created attachment 110320 [details] said problem How to reproduce: * Open kmail * move the mouse to the list view * then move the mouse to the splitter * See how the listview has a part that is rendered with the old "the mouse was over this row" color instead of with the new one Attaching screenshot, see the blueish color on top of the splitter that should not be there. Also there's xcb warnings QXcbConnection: XCB error: 8 (BadMatch), sequence: 4183, resource id: 106954838, major code: 130 (Unknown), minor code: 3 QXcbConnection: XCB error: 8 (BadMatch), sequence: 4193, resource id: 106954838, major code: 130 (Unknown), minor code: 3 QXcbConnection: XCB error: 8 (BadMatch), sequence: 4196, resource id: 106954838, major code: 130 (Unknown), minor code: 3 Disabling it, i.e. making SplitterProxy::eventFilter return false makes it go away. Using Qt 5.10
for me it's worse, I often see this rect as black on top of my message text, obscuring the mail message KMail 5.13.3 KDE Plasma Version: 5.18.3 KDE Frameworks Version: latest git Qt Version: 5.14.1
Created attachment 127089 [details] black rect over mail text
See also discussion in https://phabricator.kde.org/D10830