The step interpolator should refer to the integrator array.

This behavior will be changed later on to get immutable objects.
For now, we still rely on arrays being shared between the integrator and
the interpolator.

src/main/java/org/apache/commons/math4/ode/sampling/AbstractFieldStepInterpolator.java

@@ -79,7 +79,7 @@ public abstract class AbstractFieldStepInterpolator<T extends RealFieldElement<T
         softPreviousState   = null;
         softCurrentState    = null;
         h                   = null;
-        currentState        = y.clone();
+        currentState        = y;
         finalized           = false;
         this.forward        = isForward;
         this.mapper         = equationsMapper;