atmega16a error or just my mistake ???

I make 2 button press like this in file below, in the simulate. First, I press a top button, it show on LCD  then I press the bottom button, it the same. But if I press the bottom button first, it can't be shown on LCD display.

SimuLIDE 0.4.15
atmega16A

In the real-world of the circuit I have made, it run without problem even I press which button first or last.

I have no idea if it bug or just my mistake.
thanks