I think you misunderstand. For example when I have mouse strafing enabled, I cannot strafe right or down with the mouse or arrow keys. Left and upward strafes fine.
I think I've found the problem anyway: I had all graphics maxed out. This worked fine with small and medium sized maps, but the huge one I was using couldn't handle it. After turning down some of the graphics options it started to work again. I still have problems with it when ship numbers start to get high, but again, if I lowered the options further the problem would probably be solved.
I've just never had this as a symptom of taxed resources before.
Thanks for the response.