Okay, I will explain everything in the video,
but I swear I am pressing SPACEBAR when I show what I am doing.
I have no way of proving I am actually pressing it. But you can hear the tapping on it. I cannot jump while hugging a 1 block high wall.
It's like I am shifting on a ladder.
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Same here. It happens, when you are touching a block, having the "Up" arrow pressed and then pressing the "Jump" key: Nothing happens. However, if you release the "Up" arrow and then press "Jump", THEN you will jump. And if you again press "Up" while you are jumping you can get on top of that block.