Shops with free items: It is not a bug, it is to encourage to use troops that u normally wouldn't use, like in Jerneland there's a shop in the castle area with free peasants... you would never use peasants else...
The bug I refer to is the crash to desktop when you make right click over the Witch Hunters.
You are right about the free units. In fact, it encouraged me to use Assasins for a while.