How to define default route for Internet Sharing?

Question

I've successfully been using Internet Sharing on a MacBook Air to share a wired connection via WiFi to local devices. As of yesterday this stopped working, which may or may not be related to the recent 10.7.4 update (there are forum posts here regarding problems, but they report connection drops, not this altogether more bizarre behaviour).

Now when enabling Internet Sharing via WiFi the wired connection, promptly stops working. Some digging later and it appears the routing is messed up:

netstat -r [clipped]

Before:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            192.168.188.254    UGSc           11        2     en1
127                localhost          UCS             0        0     lo0
localhost          localhost          UH              1        6     lo0

After:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            link#5             UCS             4        0     en0
10.0.2/24          link#5             UCS             1        0     en0

As you can see, after activation the WiFi connection is being used as the default route which is clearly nonsense.

Performing a route flush resets it correctly to 192.168.188.254, however the initial behaviour must be specified somewhere. Any ideas on how to correct this?

UPDATE: It turns out this has been reported previously on 10.7.2 in this forum post, however with no solution there either.