LibreOffice toolbars & menus are rendering badly

[Borden Rhodes <jrvp@bordenrhodes.com>]

Good afternoon, list,

I'm running an up-to-date Stretch operating system on a ca. 2010 Intel
laptop chipset. I noticed last night that the toolbars and menus
aren't rendering correctly. I dumped a PNG here:
http://paste.debian.net/785668 (good for 3 days). If you can't load
the photo (because it's converted into plain text), the problem is
that the taskbar background shows artefacts from other windows. The
menus don't show artefacts but there is a delay in rendering them and
the highlight as I move my cursor over the entries.

This is the only information from .xsession_errors:

kdeinit5: PID 14789 terminated.
kdeinit5: Got EXT_EXEC '/usr/bin/libreoffice' from launcher.
kdeinit5: preparing to launch '/usr/bin/libreoffice'
QXcbConnection: XCB error: 3 (BadWindow), sequence: 58757, resource
id: 125829120, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 58762, resource
id: 125829121, major code: 18 (ChangeProperty), minor code: 0
no winId: probably startup task
Creating the cache for:
"/home/borden/business/clients/AikidoTendokai/Report.odt"
Already in database?  true
      First update :  QDateTime(2016-07-27 02:37:53.000 EDT
Qt::TimeSpec(LocalTime))
       Last update :  QDateTime(2016-07-27 17:06:40.000 EDT
Qt::TimeSpec(LocalTime))
After the adjustment
     Current score :  7
      First update :  QDateTime(2016-07-27 02:37:53.000 EDT
Qt::TimeSpec(LocalTime))
       Last update :  QDateTime(2016-07-27 17:06:40.000 EDT
Qt::TimeSpec(LocalTime))
Interval length is  0
         New score :  8
KActivitiesStats( 0x51b4640 ) ResultModelPrivate::onResultAdded
result added: "/home/me/myfile.odt" score: 8 last: 1469654190 first:
1469601473
no winId: probably startup task
QXcbConnection: XCB error: 3 (BadWindow), sequence: 59498, resource
id: 125829121, major code: 15 (QueryTree), minor code: 0
QXcbConnection: XCB error: 2 (BadValue), sequence: 48173, resource id:
121634820, major code: 142 (Unknown), minor code: 3
QXcbConnection: XCB error: 2 (BadValue), sequence: 48187, resource id:
115343454, major code: 142 (Unknown), minor code: 3

If it's not clear from this output, my desktop is KDE/Plasma 5. Is
this a known issue? I couldn't find any similar reported bugs on the
Intertubes.

With thanks,