I have a different approach
All good advice on what happened, the end caps are glued on the width and since wood expends and contacts across the WIDTH, it couldn't move. Most proper end caps are just that, loose pinned "caps" that clean up the end grain and keep the planks level, but have a tenon and groove to allow for expansion. That didn't happen.
You have 2 choices:
1. Saw off the end caps and make a tenon and a groove to allow for movement, but you still have the cross piece which won't allow for movement. dang.
2. here's the different approach.
Saw off the end caps, then saw the whole table right down the split all along the length, and reglue it. You should seal the bottom surface also.
You could leave the end caps on and reglue, 3 seams will show but the table stays the original length that way....?
If your house has major changes in humidity this won't be a perfect solution, but a "make do" fix, short of sawing apart the whole table top. dang.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 12-13-2014 at 12:18 PM.