mail locking problems

[utzoo!decvax!ucbvax!unix-wizards]

>From decvax!duke!unc!smb at Berkeley Sat Sep 26 11:27:05 1981
Full-name: Steven M. Bellovin
Location: University of North Carolina at Chapel Hill
Phone: (919) 966-3305

Several times recently, mailboxes have gotten garbled by two different
messages being written at the same time.  It seems as if the locking
protocol isn't working quite right -- we're using 4.0bsd, and the
code in /bin/mail of 4.1bsd doesn't appear to be any different.  Does
anyone have any ideas on what's wrong?