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I don't think this is a gameplay bug. It is most likely a property of your keyboard. Many keyboards lack what's called "n-key rollover", which means "the ability to register as many key-presses simultaneously as you want".

For example, if I hold z and leftarrow on my keyboard, the spacebar will be ignored. It's due to how the keyboard works technically, it just can't have certain combinations of keypresses. My keyboard doesn't have "n-key rollover".

I recommend you simply rebind the "run" button to whatever is right next to it. For me, "t" worked incredibly well throughout the whole game.