so now it´s the time to tell you why the piece cracked.
wood expands and contracts with humidity. if you take a acoustic guitar for example, and glue the top (unradiused, not domed, or anything. just flat) when the humidity is 80%, the dimensions of the wood are bigger than it would be at 40%.
so what happens is that you secured the borders of your wood to the sides, and as the humidity drops, the piece starts to shrink (in a very very small way), but the piece is glued to the sides, and not going anywhere. here is where your wood cracks. imagine yourself pulling a piece of paper with both hands. it´ll rip at some point. it´s the same with the wood, imagine that you are holding the paper very steady and pulling it tightly, if the paper could shrink, it would rip.
in my city, we get humidity as low as 13% in the dry season, you can guess when it´s the time I do more repairs to acoustic guitars. a domed top, will allow the top to expand and shrink some more (convex when it`s more humid, and getting almost flat or even concave when it´s too dry).
my advice? whenever you´re gluing wood like this, do it in a humidity controlled room. 43% is my choice. lower if its possible, but never more than that.
hope i'm being clear, english is not my first language.