The partial search uses a local Item Name Cache that only holds a certain number of item names at a time; it is populated by seeing the item, either through doing a direct search (ie. typing the whole name of the item and hitting one of the search buttons at the bottom, skipping the partial search completely), a general browse of the shops (ie. not putting any name and just using the category refinements), or by seeing it in some list, like the Scratch Prize List.
A few notes:
- This is the case on both the Global and JP versions of the game, though the Global version seems to have it occur more often from what I have seen.
- When doing a direct search, you don't have to use spaces, but you do need to make sure special characters are put in, for example, you cannot substitute an "e" for an "é".