Over the past few days I have developed a problem when moving forward and backward when using the up and down keys. The problem does not happen when using W and S, but I prefer the directional keys. The camera slowly drifts up when I press the up key to move forward, and slowly dips when I press the down button to move back. I can use the mouse to "pull" the camera to the correct position, but this interferes with my ability to play. I tested a different keyboard, and nothing changed. Any suggestions?