No one's mentioned yet that road shoes have VERY hard soles. This could be your problem as you said it was hard to walk on a hard surface. Nothing wrong at all with switching to mountain bike shoes and pedals for your road bike. The shoes are much more comfy and easier to walk in. I see people with mountain bike pedals on their road bikes often. I had Shimano SPD's when I first got a road bike so I could alternate and wouldn't have the expense of 2 sets of everything. When I decided I was 100% roadie I swapped for Speedplays and sold all the mountain stuff.