The program only wants to run once . . .

[DSMan195276]

Again:
I start the program, press the space bar, and it is displayed correctly. I start the program again, press the space bar again, and it displays "unknown". The same thing happens with "ESC".
After deleting the exe file, it works again, but only once. Then the game repeats itself. I just tried it again.

I might have an idea, do you start the program by hitting F5? If you hold the F5 key too long then the release event of F5 will go to the newly started program, that would trigger the behavior you're describing since the F5 release will be returned by _KeyHit first before the spacebar.

@Jack do you start the program by hitting the enter key on the 'Start' menu entry? -13 is an Enter key release event.