visibility

OK, I'm typesetting a work for harp and voice, and had gotten the layout/measure distribution to my satisfaction, and I was going through a final edit to render some superfluous rests in the harp part invisible, when bham! the measure distribution was all skewed. It was a pretty easy fix, but I was surprised that an element's visibility would affect the spacing (although obviously it must, otherwise one couldn't use it to create shared note-heads.)