I am using bird 1.5.0 and running OSPF along with a custom protocol which learns all routes and redistributes its routes into OSPF (import all/export all). When I restart OSPF and my protocol, I see a few times LSA ID collisions. I even tried this scenario to see the outcome : (linux box running OSPF and peering with a router where BGP routes are redistributed into OSPF).  

OSPF(bird) <-----------------> OSPF/BGP (router)

I could see a lot of LSA ID collision messages in log. I tried to debug this and realized that in some cases, the hash entry (en->nf) is NULL and we throw a LSA ID collision error. In a different scenario, I saw that the en->nf.fn was not freed from the earlier hash entry (when I print out the prefix and prefix length it is completely different than the lsa->nf.fn which results in the same error. 

I cannot recreate this scenario at will but had some success when restarting protocols or rebooting the linux box or feeding 1000+ routes (to BGP and redistribute to OSPF in router) to the setup mentioned above.

My IP address space was not overlapping either, so the LSA ID generated would have been unique. 

Also, I noticed that if I insert overlapping addresses in my protocol and redistribute to OSPF , I see LSA ID collisions (bug ?) 

Eg:

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