This isn't a bug it's the way Stacks is suppose to work. Once you click on a stack and it begins to open, it doesn't accept anymore commands (clicking) until it's fully fanned out or completely gridded. That's why when you move your mouse and click it the stack collapses. Actually, you don't even need to move your mouse. Just wait until its finished opening and then click again, voila!
Sounds to me how you want it to work is that if you accidentally click on a stack that the very next click, even if the stack is still in the process of opening, would immediately close the stack.