I suspect that the source address of your ping is not something that is routable by anything else but that new default.
XR has a nasty nature of not selecting a source address when pinging like IOS does.
IOS always takes the source addr of the interface it goes out of, XR doesn't always do that under certain circumstnaces.
That may be related.
Best way to verify that for us is to do a debug icmp on the PE that has this static route
and a show route on the source address that is recorded in that incoming ICMP request.
cheers!
xander