Per RFC 4271, Junos will tear down a BGP session upon receiving a malformed UPDATE. The issue is that Junos may recognize optional, transitive attributes that are not yet recognized by other vendors' routers. In this case, non-Junos routers which don't recognize the attribute just pass the UPDATE through with the Partial bit ON. Junos, however, would recognize the path attribute and perform validation. If the packet has errors, a Junos router will send a NOTIFICATION (Error code = 3, UPDATE message error, possible subcodes: 1, 5, or 11) and tear down the BGP session.