It depends on when it happened; if before glassing then my guess would be the Titebond II glue along with the water and the heat gun. Titebond glue is not a waterproof glue and heat can cause it to get soft.
You may be able to test the theory using some scrap stripped pieces from where you cut out for the cockpit.

Doug K.

: I went back and measured the indents. They run from 1/64 to 1/32 inches,
: which fooled me, they look worse and from 6 to 10 inches long, . All the
: indents are running along the line where the tapered ends meet the
: straight pieces, on the sides that I planed to a taper. I tried for a
: tight fit on these joints. It looks to me like the glue joint failed. I
: used Titebond II. I still would like to know for sure what happened.