Thanks for the feedback! Oh, yeah, that's definitely a bug. 

In general the mouse pointer should never end up over the tooltip overlay, but when the tooltip hits the edge of the view it stops moving, allowing the mouse pointer to move over it, preventing mouse events from reaching the button underneath. 

I've patched the code and uploaded new builds for Balloon Fight and Las Vegas  that should resolve the issue. I'll fix this in all the other simulations with the next general update (v0.9.8). 

Thanks again for reporting the issue vic :)