kwrite stops responding to mouse wheel

When kwrite is started then the mouse wheel can be used to scroll up and down.
After a while (hours?) this stops working (nothing happens when using the mouse wheel).
Scrolling by other means (keys, scroll bar) continues to work fine. So does setting position and selecting using the mouse and clicking the mouse wheel continues to paste.
I have not been able to identify any specific event that causes it to stop responding.
If I open a new window/file from an instance of kwrite that has stopped responding to the mouse wheel this also does not respond.
If I start a new instance of kwrite then this will be fine (until it also gives up) so I can have responding and non-responding instances of kwrite running at the same time.
No other application shows this behaviour.

Using Xfce as window manager.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: kwrite 4:15.12.3-0ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-83.106-generic 4.4.70
Uname: Linux 4.4.0-83-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Jul 12 14:15:45 2017
InstallationDate: Installed on 2013-08-21 (1421 days ago)
InstallationMedia: Ubuntu 12.04.2 LTS "Precise Pangolin" - Release amd64 (20130214)
SourcePackage: kate
UpgradeStatus: Upgraded to xenial on 2017-04-03 (100 days ago)