So I loaded up a copy of Ubuntu 19.04.1 LTS on my test system, and
spend the day tracking this down. Turns out to be a bug in the Color
Munki Smile driver, but valgrind only noticed if I set --redzone-size=256.
The fix will be in the next release, or a set of Beta test
x86 84 bit executables is here:
<http://www.argyllcms.com/disptools_linux64.tgz>
Graeme Gill.