Why do some of my ships list for no reason?

[Rushligh]

So, I've had this problem since i got into ksp. ( since 0.25) and it's finially gotten to me.
Often, when using OPT parts, but sometimes not, my ship (SPH) spins to the right and looses complete control.
Using f12 to check my aero forces there is nothing out of wack. the ship is completely symmetrical, engines are thrusting equally and not off center, RCS is on and operational, all control mods are off, SAS is on.
Just to test it i strapped on a tonne more RCS units (Electric thrust thanks to Starlion and KSPI) and got it into space. with no aero interfierence, no rcs or engine thrust, no reaction wheels, it begins to spin and accelerate till the camera wobbles and blurs then the ship explodes from GForce.

I've dissembled the entire thing in SPH and re-assembled it to make sure there's no asymmetry or duplicate parts (2 identical parts inside each other caused when using symmetry wrong), and it STILL SPINS.

Halp ;_;

[soulsource]

You might have accidentally enabled control trim. To reset trim, press Mod+x (where Mod is ALT on Windows, and Right-Shift on Linux). See http://wiki.kerbalspaceprogram.com/wiki/Key_bindings for details.