nevermind
Previous behavior in 3.1.0 release e26f7c4 was that applying a volta to a multi-measure rest would be that the multi-measure rest wouldn't be broken apart.
However now in 3.1.0 currently master 3543170, I'm observing that the multi-measure rest gets broken up such that the final measure of rest gets split into its own measure, separated from the prior measures of the multi-measure rest which remain together as a multi-measure rest.
Nevermind...somehow I was looking off the wrong branch.