Using the ICE-4565 regression test, it's clear to see that the value of the redirect upate returned by MyFaces uses the .xhtml extension:
<?xml version="1.0" encoding="utf-8"?><partial-response><redirect url="/my/page.xhtml"></redirect></partial-response>
rather than the .jsf extension that is declared in the navigation rule
<navigation-case>
<from-outcome>submit</from-outcome>
<to-view-id>/page.jsf</to-view-id>
<redirect/>
</navigation-case>
With Mojarra, the extension is preserved:
<?xml version='1.0' encoding='UTF-8'?><partial-response><redirect url="/mo/page.jsf"></redirect></partial-response>
Linking to parent case.