How can I highlight the current navigation item when viewing the store?

I am trying to add css styles for the navigation menu, specifically when an item is 'current'.

This works by wordpress detecting if the page is a child of a menu item, and giving it a class of 'current-item'.

However this does not work with any MarketPress pages past the top level ('/store').

Is there any way to:
a) invoke this,
b) programatically work around this, and/or
c) get this developed in a future upgrade?

Thanks