When you Lean (Q and E) your aim does not change to be relative to your perspective.

Whenever you lean, aiming remains oriented in respect to the ground, not your lean angle. IE: if you lean left and then try to aim up, your reticle feels like its aiming up and to the right because it moves vertically with respect to the ground, not your perspective. It has similar effects to aiming horizontally while leaning. It feels disorienting and makes it difficult to quickly aim and shoot while leaning around a corner.