It is a common misconception that tab structures need a case structure on the diagram to keep the universe in balance. This is wrong!
Remove your case structure and don't even look at the tab terminal on the diagram. You don't need it. In this case, a tab control is just a way to more logically organize the front panel.
To fully understand what your problem is, run while looking at the block diagram with execution highlighting. Putting an event structure inside a case seems like a very bad idea in general, but please post your code so we can see where it sticks.