I am using bro 0.7a48 version on openBSD 2.9.
First thing to try is the latest alpha snapshot:
ftp://ftp.ee.lbl.gov/.vp-bro-pub-0.7a90.tar.gz
If it still occurs with that, then see if you can get a version of the problem
to reproduce (by capturing the related traffic in a tcpdump save file).
Vern