Hi,
Please check F4 Help Settings.
Since you might have a lot of Item Category and the search help is different between WEB UI & GUI it might be the case that the system search in table of item categories with a MAXROWS = VALUE.
I did found the case in my system that if I had it in 500 The last 9 item categories of a document was not being shown in my search helps because the table had 509 rows.
It sounds ridiculous but It is not.
Regards