When I play "kurve" there are times when the screen gets stuck and I cannot make progress. This has happened earlier also, but today I noticed this particular keystroke which made this happen.
I noticed that when I press the "left arrow" on the top left cell in today's scheme, this happens. Maybe, its happening only for me.
Similarly, kakurodoku gets stuck many times for me but I do not know the exact reason/keystroke for that. Generally, it gets stuck right at the start.