I am not sure if I can get an exact proof, but every time you buy something on the store, it refreshes and you lose any custom search you had selected. It's probably not game breaking, but it is annoying when buying multiple things.
-Select a custom search (Not necessary but allows you to notice it easier)
(The store will now refresh and you have to do your search again)
*It also seems to happen even when you get gifted.