qmlscene -style Material says Material is not supported (but env var works)

qmlscene -style material file.qml

prints

QApplication: invalid style override passed, ignoring it.
Available styles: Windows, Fusion

But this is clearly documented as the preferred way to try different styles (see docs for using-styles-in-qt-quick-controls-2).   However, even though the above error message appears,  the Material style does in fact seem to be used.     No error occurs if the Windows or Fusion style is specified, only Material.

So something must be wrong with the configuration which prevents qmlscene from realizing that the Material style is available.

Note: Using the environment variable method works without error:

QT_QUICK_CONTROLS_STYLE=Material qmlscene file.qml

STEPS TO REPRODUCE (using /usr/bin/env to avoid extraneous inflences):

1. env -i DISPLAY=$DISPLAY PATH=/bin:/usr/bin XDG_RUNTIME_DIR=$XDG_RUNTIME_DIR /path/to/Qt/5.12.1/gcc_64/bin/qmlscene -style material file.qml

This was using a new, clean install of 5.12.1 alone.