[kmail2] [Bug 359823] New: Scrolling in message view window only updates window partially

[Stephan Diestelhorst via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359823

            Bug ID: 359823
           Summary: Scrolling in message view window only updates window
                    partially
           Product: kmail2
           Version: 5.1
          Platform: Kubuntu Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: NOR
         Component: UI
          Assignee: kdepim-bugs at kde.org
          Reporter: stephan.diestelhorst at gmail.com

After a while of using kmail (5.0.2 KDE Frameworks: 5.15.0, Qt 5.4.2), it seems
that the message preview below the message list stops scrolling properly.  I
can still scroll, but if I scroll down, only the lower ~50 pixels (~2 lines of
text) get updated.  When I scroll up, it is only the top 50 pixels in that
window.  The rest stays exactly flat.

I have tried disabling Desktop Effects (Alt + Shift + F12), but that does not
resolve the problem once it has occurred.  I also played with the KDE
compositor settings and selected all different tearing options, GL versions
etc, but nothing helped.

The only way to fix this seems to be to restart KMail for now.  Then it
continues working for a while, I have not yet identified when this happens.  I
usually can work for (felt) 30 mins to several hours until this turns up again.

This happens for both HTML and text emails.  Going to the next message will
render the full view correctly.  Resizing the preview pane does not have an
effect, other than temporarily rendering the screen correctly.

Reproducible: Always

Steps to Reproduce:
1. browse emails and use the preview window and scroll
2. do this for a while
3. observe the scrolling not affecting the middle of the window

Actual Results:  
the middle of the rendered email does not move on the screen

Expected Results:  
the entire message scrolls up and down

kubuntu package: 4:15.08.2-0ubuntu1

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