Bro always crashes

without seeing a SYN-ack from B.80 in between. This then leads to
Bro holding state for the half-established connection after it sees
A.1234 -> B.80.

I should add that I diagnosed this because the connection summaries
Bro generated on stdout looked like:

925897359.600000 0.26 http ? 1775 SHR X

"SHR" indicates a half-stablished connection that was closed by the
responder. (It's the responder in this case because the only packets
Bro saw were the SYN-ack [rather than the SYN] and the FIN.)

This is a highly unusual state for normal traffic, i.e. when Bro sees
both sides of the connections.