I built a dresser last summer out of white oak. Just now the two pieces I used for the top are separating. I used cookies and on the underside I used several cletes both glued to each peice of the top as well as screwed everything together. I finished the top with urathane and the underneath was stained but not urathaned. Why did this problem occur and how do I fix it and also how do I avoid the same thing happening on my next project? Is the humidity or lack of it that is causing this. I thought that since I started with rough sawn, kiln dried lumber and sealed every inch of it I could avoid this but it seems not. Any information and help would be appreciated.