User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:47.0) Gecko/20100101
Firefox/47.0
Build Identifier: 

Ever since booting up today, mouse wheel events in Plasma 5 sometimes get sent
to the wrong window.

When I use the mouse wheel to scroll the content in any window that allows
scrolling, scrolling will work for some time until suddenly, quite randomly,
some other open window will start scrolling. For example, when scrolling in
Firefox, suddenly instead of the Firefox window keeping on scrolling, the
Konsole window next to it will scroll through its command history. A lot of the
time, the scroll events seem to erroneously go to the window list or the
desktop, meaning I end up switching through the open windows or the virtual
desktops.

This only started happening today, but unfortunately, I cannot say which update
might have brought this on, since I hadn't rebooted in some time (weeks, maybe
a month) before that. (I am using OpenSuse in VirtualBox, and I usually just
freeze the VM instead of doing a real shutdown. I did a real shutdown yesterday
because there was a kernel update.)

I am not moving the mouse out of the window I am trying to scroll or otherwise
making it lose focus. Scrolling using the arrow keys works or by dragging the
scroll bar works fine.

Reproducible: Sometimes

Steps to Reproduce:
1. Have several windows open that allow scrolling using the mouse wheel.
2. Move the mouse cursor into one of those windows and activate it (if not
using focus-follows-mouse anyway).
3. Scroll the content for a while, back and forth, without moving the mouse
cursor
Actual Results:  
The selected window may scroll is content for some time. After some time, or
sometimes immediately, other windows will start scrolling instead, or other
windows will get brought to the foreground and start scrolling or the virtual
desktops will be switched.

Expected Results:  
As long as the mouse cursor stays in the original window, the mouse wheel
should only scroll content in that window, never in any others and never the
window list or the virtual desktops.

OpenSuse is running in a virtual machine under VirtualBox, in turn running
under MS Windows 10.

The problem has never occured before this morning, but since then has been
persistent.