Doesn't work with CupertinoTabScaffold

[traed]

Using onGenerateRoute and MaterialWithModalsPageRoute, if the builder returns a CupertinoPageScaffold everything works as in the examples, but if it returns a CupertinoTabScaffold the background doesn't animate (shrink). If I wrap the CupertinoTabScaffold with a CupertinoScaffold and use CupertinoTabScaffold.showCupertinoModalBottomSheet the background shrinks but the modal is contained within the shrunken background instead.