[Mimedefang] Apostrophes escaped in "To:" address

[Patrick Morris]

I've got a user complaining that mail sent to addresses like 
"Sean.O'Leary at domain.com" are being mangled in transit, and getting 
handed off to the recipient as "Sean.O%27Leary at domain.com," and bouncing.

After some log wrangling, it looks like they're coming out of MIMEDefang 
that way.  As far as I can tell, apostrophes in mail addresses don't 
break any RFCs.  Can anyone recommend anything I can do to make 
MIMEDefang leave these addresses alone (or at least re-percent_decode 
them on the way out)?