Spatial lookAt + assertion error

When assertions are enabled, whenevery ou use lookAt() in a spatial extending class the came just crashes with a assertion error caused by itself:


public void lookAt(Vector3f position, Vector3f upVector) {
        if ((refreshFlags & RF_TRANSFORM) != 0){

        assert TempVars.get().lock();
        Vector3f compVecA = TempVars.get().vect1;
        getLocalRotation().lookAt(compVecA, upVector); //this here has to fail, as quaternion.lookAt tries itself to call lock()
        assert TempVars.get().unlock();


 public void lookAt(Vector3f direction, Vector3f up ) {
        TempVars vars = TempVars.get();
        assert vars.lock();  //this here has to fail of course then...
        vars.vect3.set( direction ).normalizeLocal();
        vars.vect1.set( up ).crossLocal( direction ).normalizeLocal();
        vars.vect2.set( direction ).crossLocal( vars.vect1 ).normalizeLocal();
        fromAxes( vars.vect1, vars.vect2, vars.vect3 );
        assert vars.unlock();