Headcrab has posted a thread to modns.org which claims to provide a solution to PSHB:

http://www.modns.org/forums/index.php?showtopic=660

PSHB stands for "Player Specific Hitbox Bug", and I think we've all experienced it. We've certainly discussed it here in the past.

I've incorporated the above correction for PSHB into our server. Folks seem 100% confident that this fix corrects one predominant method by which a person can acquire PSHB. What I don't read is anyone saying with 100% confidence that this method is the only way for someone to acquire PSHB.

Hopefully this will be the end of PSHB on our server.