[PLUG] Diagnosing/fixing fontconfig error

[Rich Shepard]

When I shut down X Windows on the Slackware64-14.2 desktop, among all the
notices on the console are a bunch related to fonts. They start as:
 	fontconfig error line 162: mismatched tag
 	cannot load default file
The last line is repeated multiple times.

This same error just popped up when I ran a small PyQt5 app.

How do I determine which of the very many fontconfig/ directories has a
mismatched tag on line 162 and how do I identify the default file?

TIA,

Rich