If I understand correctly, your regulator was working fine prior to this dive, it had a problem in current, but it worked fine later. I have to agree with your original suspicion re the exhaust diaphragm became unseated in the current. It could be as Matt suggested a bit on the thin side, or it could actually be the wrong diameter. If it was replaced with a generic one during it's last rebuild, the one installed may be working fine until you are in a current.
Here is a link to a few other checks you can perform including a water tight check.
http://www.scubaboard.com/forums/4320058-post14.html
Keep us posted on your findings.
Couv
Here is a link to a few other checks you can perform including a water tight check.
http://www.scubaboard.com/forums/4320058-post14.html
Keep us posted on your findings.
Couv