Bill Tindall
There is stress locked into these lumber. It is common with thick oak because oak must be dried very slowly and sometimes it isn't. Because you see it on most all of the lumber it is a drying defect not stress as a result of some aspect of how the tree grew. This sort of stress can only be relieved by steaming the lumber, a process that will soften the fibers and let the lumber relax.

I discussed some of the reasons how lumber gets stressed in a post about a week ago but I don't recall the post title.

I hope I am interpreting your question correctly. You are in fact ripping the board into two more narrow pieces? Rsawing usually means ripping the board into two thinner pieces of the same width.