If you mean that compositor is supposed to then repaint what is behind our now-transposed window, then it is what happens most of the time, but also does not necessarily happen if what was below our window transparent pixels was wrongly overwritten doesn't paint anything on repaint. It is certainly a subtle difference and if what is behind is not going to be repainted it is not going to look very well in a generic case anyway. But also it is correct not to paint pixels we should not; it is a very simple change not introducing any complication; it is how that was done before.