Originally I found the issue while playing about in imagemajick which would produce an error like this.
"Fontconfig warning: "/etc/fonts/conf.d/53-monospace-lcd-filter.conf", line 10: Having multiple values in
isn't supported and may not work as expected"
You can reproduce that error using this command;
So, I opened up the file referenced in the error and found it was an XML file.
In the element test name="family" there were two fonts configured, in my case these were "DejaVu Sans Mono" and "Bitstream Vera Sans Mono".
Now, considering that the error was complaining about not liking having two values present, I decided to remove one. I removed the second one.
After doing that things behaved in much more polite way;
DejaVuSans.ttf: "DejaVu Sans" "Book"