Text type case is not previewed in the text sample widget

[DelazJ]

Open Style Manager and add or edit a text format
At the top of the dialog, The "text sample" widget provides a preview of the settings
In the Formatting tab, change the "Type case". Nothing happens.

It used to work (a screenshot from a recent version)

QGIS version	3.15.0-Master	QGIS code revision	61a1801
Compiled against Qt	5.12.8	Running against Qt	5.12.8
Compiled against GDAL/OGR	3.0.4	Running against GDAL/OGR	3.0.4
Compiled against GEOS	3.8.0-CAPI-1.13.1	Running against GEOS	3.8.0-CAPI-1.13.1
Compiled against SQLite	3.31.1	Running against SQLite	3.31.1
PostgreSQL Client Version	12.4 (Ubuntu 12.4-0ubuntu0.20.04.1)	SpatiaLite Version	4.3.0a
QWT Version	6.1.4	QScintilla2 Version	2.11.2
Compiled against PROJ	6.3.1	Running against PROJ	Rel. 6.3.1, February 10th, 2020
OS Version	Ubuntu 20.04.1 LTS	This copy of QGIS writes debugging output.
Active python plugins	db_manager; MetaSearch; processing