How do I change Shop Menu (sub-pages) setting?

I am having a problem with how the sub-pages are showing up for the Shop page on my main menu. They are directly under the parent tab on my menu, instead of being hidden until you mouse over (or click) the "Store" button. I experimented with other shopping cart plugins before I settled on MarketPress, and this wasn't an issue with the others I tired, so it seems like a default setting or something in MarketPress rather than my theme. Any thoughts on how I can fix this?