I'm not sure if this is some setting I've missed, but if it is, it is completely non-intuitive to me.
I am removing a person swimming in the water; pretty easy clonestamp with some manual keyframing of its position and clone position. However, I notice the duplication (who knows if a regular person would? but its the editors curse) and would like to offset it by a few frames. I assume Clone Time shift is the way to do it; it would simply shift the clone source by however many frames I indicate, right?
However, changing Clone Time Shift by any amount appears to be freeze-framing the layer! No matter the amount, it all changes to the same frame, with the clone stamp effect still intact, though.