I just stumbled upon the same bug - 1) first I see the blue arrow, 2) when I run the program, it disappears but still works, 3) when I stop the program, it is invisible, 4) when I rerun, it is still invisible, but still works (same as 2). Exiting and reentering the level makes it visible.
Edit: and now an even weirder version of it - here a downward hollow blue arrow turn into a rightward hollow red arrow (but still works as intended). If I move the fake red arrow and launch, it still behaves as if it was a downward blue one. Replacing it with a rightward white one creates an addition white arrow pointing downward, both real.