designer-qt5 seg faults when invoked

[Rich Shepard]

I run Slackware-14.2/x86_64 on all hosts. This desktop has installed
qt-4.8.7-x86_64-4, qt5-5.12.8-x86_64-1_SBo, qt-creator-4.12.3-x86_64-1_SBo,
PyQt5-5.13.2-x86_64-1_SBo, and python3-PyQt5-5.13.2-x86_64-1_SBo. Perhaps
the last two conflict and cause the problems I have trying to load
designer-qt5.

I haven't found a Qt maillist so I hope it's appropriate for me to ask for
help here.

I'm building my first PyQt5/Python3 application; a front end to the business
management database I've used with the psql shell for several years to track
my business development efforts.

In /usr/bin/ there are the Qt4 and Qt5 designers: /usr/bin/designer ->
/usr/lib64/qt/bin/designer* and /usr/bin/designer-qt5 ->
/usr/lib64/qt5/bin/designer*. The former loads, the latter seg faults when I
try to load it:
$ designer-qt5
Segmentation fault

I've no idea how to figure out why this happens. The seg fault signal
provides no clue regarding what caused the problem. I'm asking for
suggestions, recommendations, advice, and other help to resolve this issue.

TIA,

Rich