Gumption trap update: Solved the problem, finally. I introduced a temporary global variable and pointed it to the offending object; adding a watch on this global variable helped me identify the exact line of code that caused the original object's value to change mysteriously. To my surprise, this was the creation of another unrelated object (although, to be fair, both objects were of the same class). Simply adding an empty constructor to that class' definition made the problem go away. From the look of things, I am probably missing some not-so-subtle point regarding constructors in C++...