Quote from sandlapper "It sounds like replacement is necessary. If/when you talk to a cabinetmaker, just explain what has happened and quiz him on his construction techniques. The grooves in the frame must be deeper than the panel is wide to allow for the expansion."
If you do go to a cabinet maker, a knowledgeable one will make the grooves deep enough and also stabilize the panel in the center using small rubber spacers that allow expansion but hold the panel centered in it's frame. If the frame came apart at the joints, there was simply not sufficient room for expansion. Wood expands more width wise than length along the grain, so the Rails (top and bottom) won't expand as much as the panel.
AS seems to have stopped using Hickory???? May because of this problem. Hickory and Oak move more than Maple and others as to expansion due to humidity, but not excessively so, and about the same amount.
You absolutely need to coat all surfaces equally to mitigate differential expansion between finished and unfinished faces. Properly made table tops are carefully laid up to counteract the tendency for wood to curl with the grain. This degree of attention is not going to be found in commercial construction unfortunately, but equal surface treatment can help a lot.