[c-nsp] Can't ping outside network over T1

[Todd Shipway]

I've got a weird issue that I can't seem to solve.
Overview.  Network is running on a core router which is a 7513 with
channelized DS3's split into ds1's to customers.  I have one customer who
has 2 T1's bonded using multilink ppp.  I can ping everything on our
network, including other customers.  But nothing is making it out of our
network to our peers.  I've moved the t1 to multiple cards and interfaces.
 Separating the T1's works fine, but multilink kills the public routing side
of it, even when the source IP is a public address that routes fine on a
single interface.

Any ideas what may cause something like this?  I've got a ton of other
customers setup with this identical hardware and configuration working fine.
 I've also swapped out hardware at the remote end as well.