The recommended in the store.

So I recently went into a game as lulu. I used my AP rune page and I also used the masteries I usually set for her. The thing is when I went into the store it gave me support items. It was the first time that happened while using those masteries.

My question is what actually decides what type of items show up in the store. The same thing happened when I tried Kayle support. It gave me the standard AP items. I don't remember all the items I usuallly get so it's very annoying to have to spend time in the store to search for the items because the game decides when it thinks I am support.

Also is there a way I can switch the recommended items in-game? I saw it once on a video on this neat website called YouTube. How can I do this if I can do this.