Fermatas prevent hiding of staves
In any kind of multi staff work, if you add one fermata, you add a fermata to every single staff of that measure. MS3 unhides staves with fermatas, which means that any fermata added to a work renders 'hide empty staves' a rather pointless option and wastes lots of trees and ink.
Rite of Spring is a little nutty on the 'number of staves' side, but Stravinsky is hardly the only composer that calls for such an army of instruments that one cannot fit it all on one page without staff hiding or very vigorous staff merging.
There is no workaround for this that I know of, but while this is a problem in MS3, it was not in MS2.3.2