Unis-labels and hiding staves

After a divisi section: in order to automatically hide subsequent empty staves unis."-labels must be placed at the end of the last divisi-measure and not at the beginning of the subsequent (unis.-) measure.; if placed there hiding of following empty divisi staves is prevented – why?

The first divisi change on a system determines the number of staves shown in that system, including a prevailing divisi change that started on a previous system, but was still in effect at the start of the system.

The sooner you return to unison, the sooner you make it possible to show one staff rather than two (or however many staves there were in your last divisi change).

I see; it is just a bit confusing in galley view .