Unchecking 'Create courtesy clefs' hides all clefs at the beginning of a measure
Instead of hiding additional clefs at the end of a system all clefs at the beginning of a measure are hidden.
Steps to reproduce
Add a clef change to a measure in the middle of a system line.
Uncheck Format > Style > Page > 'Create courtesy clefs'
The added clef will vanish while the notes sound as if the clef would be there.