IDE source scanning cannot be disabled with qt-configure-module

Note:
Scanning for ide sources...
Please note configure can execute faster if called with:
 'qt-configure-module path/to/src -- -DQT_SHOW_EXTRA_IDE_SOURCES=OFF' 

And yet I've got that argument in my config.opt for both this modular build and the installed build I'm calling `qt-configure-module` from.

This message comes from within webengine's cmake.