As the title says, rendering can slow down from 16m rays/s to less than 1m in this sample scene. It happens if you rotate parent object or the instances itself through the transformations menu. Strangely enough, if you rotate parent object and then the instances by the same amount in the opposite direction, there's no slowdown. It seems that rendering is only affected when geometry is rotated relative to the global scene coordinates.
Everything has simple gray material and is lit by corona scene environment to eliminate unnecessary variables.
