In my experience this is a glitch that happens if you’re using a mac that happens to have a trackpad. For some reason the trackpad messes up the input. I just noticed this when I was playing GW2.
It was fine with my MBA in clamshell mode, using an external display but…
when I unhooked the display and tried running it with the laptop screen (to see what, if any, FPS boost I would get), the camera went screwy.
So…the fix. depending on what operating system you’re running it’ll be slightly different, but essentially you have to make your computer ignore the trackpad when a mouse is present.
Open System Preferences
Select Accessibility (if you’re running Snow Leopard it’ll be called Universal Access instead)
Choose Mouse and Trackpad from the side menu
Check the box: Ignore built-in trackpad when mouse or wireless trackpad is present.
Reboot GW2
Enjoy!