I am curious about the milling operation. In your picture, it appears that you were machining from right to left and attempting to remove .030 of material. Is that correct?
If so, the surface of the plate that you are milling needs to be just above the vise, with the absolute minimum stick-out.
If I am correct in my assumption about what type of milling operation you were doing, and you pumped the oiler while doing so, the only real explanation is that you "hydraulically" lifted the table slightly when pumping the oiler. When I owned my 833T, I found the gibs to be of marginal quality at best. Might want to reexamine the gib tightness and fit on the table.