I want to force the use of png-Icons instead of the svg-icons and therefore set $CFG->svgicons to the boolean false in my config.php. This didn't work as expected, as all values of $CFG will be casted to string through the call to "initialise_cfg()" and its call to "get_config('core')" in setup.php, while the method "theme_config::use_svg_icons()" expects $CFG->svgicons to be of boolean type.

The bug lies in "use_svg_icons()" as the global policy seems to be that every configuration value will be of type string. But it still made me doubt myself for a moment or two when I put a value of one type in and it magically transformed into a value of another type.

I only checked for version 2.9.1 but I suspect previous versions will also be affected.