It would appear that the new version of OH, which should allow all VR applications to be started from within its library, is not recognising FI XP and is instead creating a library entry that points straight at the XPlane executable.
I have reported this in the appropriate thread on the Oculus forum, but it might be a good idea if others could add a little further weight to the request for a fix.
You can still run it the old-fashioned way, so no real panic.