Sorry for this late followup. This thread was just brought to my
attention.
Sounds like the cisco bug which has affected several different providers
over the last month or so. A route (almost always a high-interest
destination) doesn't get added to the forwarding table correctly.
Not true. The fact that none of my colleagues, the isp team, and I
was contacted/involved seems to suggest these routers do not run
Cisco IOS.
-- Enke