I am using left shift.
So, should I be able to jump while running?
*edit*
Just did a little test in a text document.
when i hold the left shift, up arrow and press the space bar it doesn't register as a key press.
So i remapped jump to "W" (on a azerty keyboard, that's Z on a qwerty) and that works just fine.
So it seems to be a hardware problem....