Bug 414955

It is reported as Debian Bug: https://bugs.debian.org/946365

KMail also stops responding when the pointer changes, e.g. to change the size of the panes.

When opening Kmail on Wayland without any adjustments, then the preview window is blank or just a black frame.

Operating System: Arch Linux 
KDE Plasma Version: 5.18.0
KDE Frameworks Version: 5.67.0
Qt Version: 5.14.1
Kernel Version: 5.5.3-arch1-1

I can also reproduce that KMail and Kontact become unresponsive when the preview pane is active. With preview pane I mean the Qt WebEngine based preview of the mail. (I hope the author of the issue means the same.)

In my case the QWebEngineView is completely transparent.

The problem seems to be specific to:

* Using Wayland natively; it can *not* be reproduced using XWayland via `kmail -platform xcb` or using a  regular X session
* The way how KMail embeds the Qt WebEngine frame; when opening a mail in a separate window the problem can not be reproduced. There seems to be something special KMail is doing here. A tag editor I've developed embeds a QWebEngineView using a QSplitter as well and it works fine under Wayland.

I'm using Arch Linux (x86_64) with Intel Graphics:

```
pacman -Q kwin plasma-desktop plasma-workspace kmail kparts qt5-base qt5-webengine qt5-wayland wayland wayland-protocols linux-zen mesa 
kwin 5.18.4.1-4
plasma-desktop 5.18.4.1-1
plasma-workspace 5.18.4.1-2
kmail 20.04.0-1
kparts 5.69.0-1
qt5-base 5.14.2-1
qt5-webengine 5.14.2-1
qt5-wayland 5.14.2-1
wayland 1.18.0-2
wayland-protocols 1.20-1
linux-zen 5.6.7.zen1-1
mesa 20.0.5-1
```

I've just wanted to write that the problem is gone on my system after updating. Unfortunately that's not the case after all. So the problem is simply not 100 % of the time reproducible. In this case I've started kmail and it worked. Then I closed it to test kontact and it ceased to work. When going back to kmail it was now broken as well.

So the problem is still present in these versions:

```
pacman -Q kwin plasma-desktop plasma-workspace kmail kparts qt5-base qt5-webengine qt5-wayland wayland wayland-protocols linu
kwin 5.18.5-1
plasma-desktop 5.18.5-1
plasma-workspace 5.18.5-1
kmail 20.04.0-1
kparts 5.70.0-1
qt5-base 5.14.2-2
qt5-webengine 5.14.2-3
qt5-wayland 5.14.2-1
wayland 1.18.0-2
wayland-protocols 1.20-1
linux-zen 5.6.12.zen1-1
mesa 20.0.6-2
```

Let me know if there's more useful information I could provide. (stderr/stdout of kmail doesn't provide any clues.)

I can confirm this bug, or something similar. I'm using Wayland with Kubuntu 20.04. Practically every application works, except the preview in KMail.

With preview disabled, KMail works fine.

With the preview enabled, the whole desktop does a range of strange things:
- it copied (part-)images of the last website I visited on Firefox and also my desktop image to the preview pane. Sometimes also just a black rectangular.
- then it turned the cursor into a horizontal resizing tool, with KMail, however, becoming completely unresponsive (but not crashing)
- when I tried to change the settings in KMail, it startet "mixing" the two windows: the normal message list and the settings window. Parts of the settings window could be seen, superimposed on parts of the normal message list.
- it was difficult to navigate to minimized windows in the window bar, because the little rectangulars started to flicker or disappear for a few seconds when I tried to access them.
- the KMail window resized itself, growing increasingly larger on the right-hand side with each fresh access, so that the "close" cross couldn't be accessed for closing the application.

Strangely enough, each time I opened KMail again, the problem was different, just a whole range of strange behaviours.

Steps to reproduce:
Start Kmail on wayland-plasma with active preview pane in Kubuntu 20.04.

Observed result:
See above; in my case, KMail remains responsive most of the time. If it does go grey and does not repspond, I can still close it via the icon at the top right-hand corner. If I can't see that icon (resizing; see above), I can still move the whole window to get at the cross icon.

Expected result:
Normal message list; stable desktop.

I confirm the bug (or a avery similar one): kmail stop responding when the cursor shapes changes (e.g. when I hoover over a resizable border).


SOFTWARE/OS VERSIONS
Archlinux, with intel graphics.

kwin 5.18.5-1
plasma-desktop 5.18.5-2
plasma-workspace 5.18.5-3
kmail 20.04.1-1
kparts 5.70.0-1
qt5-base 5.14.2-3
qt5-webengine 5.14.2-3
qt5-wayland 5.14.2-1
wayland 1.18.0-2
wayland-protocols 1.20-1
mesa 20.0.7-3

Ditto. KMail hangs with an unresponsive window as soon as it opens on Wayland (running on Debian bullseye). It also seems to affect Kontact, which also hangs within seconds of opening. No error messages.

This is resolved with KMail 5.15.3 (20.08.3), on KDE Frameworks 5.77.0 and 5.15.2; Debian Bullseye.