Differences in behavior (other than timing) between debug code and non-debug code are almost always due to pointer problems. Have all pointers been properly initialized? Are array bounds being violated? Can two routines update a pointer so that one is using a no longer valid pointer?

Note that if you have pointer problems, they still exist in the debug code, although they may not manifest themselves, at least not frequently.

Any manager who would ship debug code on the basis that "it works ok", when the optimized code doesn't, should have the letters I, D, I, O, T carved into his forehead. Then he should be fired.