I have the same issue. Google is selected as my defualt browser but it still searches in Yahoo. Even when I type in the search bar at the top of the "Speed Dial" page, which has the Google Icon next to it it still searches in Yahoo. I've tried chaning it back and forth but no luck.
I've also noticed something else strange. Whenever I search something it closes the tab and opens another tab to the left of the previous tab (if I have multiple open). Idk if this is in some way related.