Not necessarily an easy fix. Having just pondered this, the issue might be that once the IR illuminator is on, the scene is brightly illuminated, at least as far as the camera is concerned, so it can’t ‘see’ the provision of white light. Just a guess really, but has some logic to it. Possibly backed up by the fact that it’s really hard to tell that the white light has even been turned on, when watching the recording back, so from the camera’s perspective, little to nothing changes.
Either way, good luck getting this implemented, because few customer requests ever come to fruition, but yes there is a thread for such suggestions.