I have no idea. It is true that BIRD does not check checksums of LSAs later when they are stored, but it checks that when it receives them. If you did restart of a BIRD (or at least OSPF protocol) then no bad LSA could survive that. It might be useful if you could get a tcpdump copy of the OSPF communication [*] on the problematic link (when there is a problem). and output of 'show ospf lsadb'.
[*] tcpdump -i ethX -s 0 -w dumpfile ip proto 89
I am not quite sure if it is LSA checksum. I don't have tcpdump stored anywhere, because I was watching it "live", but it looked like RouterOS had a problem with Hello packet itself. The moment I've seen Hello packet broadcasted to the link, the wrong checksum entry poped in RouterOS logs. -- Adrian