I have a page "P" with an icon specified via {{#titleicon_file:P-image.png}}, and it belongs to category "C", which also has a different icon specified via {{#titleicon_file:C-image.png}}. On page P, both C-image.png and P-image.png show in the title, so I added {{#hidetitleicon:category}} to P.
But both C-image.png and P-image.png continue to appear in the title of P. What am I missing?