Is the target supposed to lock whenever the turbo mode is in affect? Because that's what's happening to me.

Yes, you cant change direction when turbo-ing

tikki_tikki2000: what key(s) do you have bound to turbo?
(you can find out by typing "/print all" [without quotes] in chat, by going to Options/Controls/Keyboard in the start-up screen or ESC/Options/Controls/Keyboard in-game.)

I can change direction, it's just the crossfires that lock.

Actually what happens when you move your mouse is your camera angle changing. The crosshairs that you refer to is the direction your ship is pointing.