It's your keyboard. My laptop has a similar issue. Keyboards are wired so you can only hit so many keys at a time. Sometimes it's just two, sometimes you can hit 4 or 5 at once, depending on which keys they are and how your keyboard circuitry is wired.
You have two options:
a) Get a different keyboard.
b) Bind a different set of keys for movement.
"a" wasn't an option on my laptop, so I just shifted all my binds over one key and they worked.