Bill Tindall
Again if I understand correctly Ed was in fact resawing the board into two thinner boards and the resulting thinner boards cupped. Cup is across the width of a board; bow is along the length.

Cupping can result from two processes that can be distinguished by how quick it occurs.

If the resawed pieces cup immediately after resawing it is a result of the lumber being stressed. The most common cause of stress is drying, (either air or kiln) the lumber too fast. When dried too fast the interior of the lumber is under tension. When resawed this tension pulls the thinner boards into a cupped configuration. It is very easy to dry oak too fast because of how it dries and the requirement to dry oak very slowly. Stress can also occur from how a tree grew but this isn't the cause of Ed's problem.

If the lumber cups after a day or more, it is because the lumber is gaining or loosing moisture from one side faster than the other. There may have been a moisture gradient across the thickness of the thick piece. Or the resawed lumber may have been stored in a way where one side gained or lost moisture faster than the other.