Maybe try switching the screen between fullscreen and windowed mode? That might help. Either way, I've never heard of that specific problem, so I'm sorry I can't provide you with specific help.

Did you find a fix for this? Because I have the same problem and it makes the game unplayable. If someting lies on the ground next to the edge the character only walks backwards when I try o pick it up. I attached a picture of what it looks like. I tried minimizing/maximizing and playing in a window, but nothing helps.

Edit: Turns out disabling mouse movement ("floating cursor") fixes it. Which makes me wonder why it's even in the game and how they didn't notice this problem...

I don't think so.. It was with my laptop.. I've since gotten another PC and I don't have that issue with it.

I think it was to switch the video mode to DirectDraw instead of OpenGL and playing in a window (I had to get it to work properly with Fraps, which requires a 3D mode).

I had this exact problem myself, trying to pick up small objects like rocks would move you backwards instead. As mentioned by Threedots, you'll need to go into options and turn off the Floating Cursor option. I ended up playing the whole game without it, using the arrow keys on the keyboard for movement and clicking the arrows on the left of the screen to turn.