Could be tranplant stress where the roots did not take hold over a dry period of time in '05. That year a large established 35 foot Maple between us and our neighbor's succumbed to stress from being cut back combined with the long dry stretch between April and August(it was not watered). It could also be damage to the tree as you described the bark's state.

If the bark damage tended to be on the side receiving the most direct sun, it's possible that a tree transplanted from a shady area suffered winter bark split in a sunnier location. Most Japanese maples have relatively thin bark and can be prone to this problem.