From the release announcement (see bug URL):

- Message address fields are now parsed differently, fixing some
  issues with spaces. Affects only clients which use FETCH ENVELOPE
  command.
- Message MIME parser was somewhat broken with missing MIME boundaries
- mbox: Don't allow X-UID headers in mails to override the UIDs we
  would otherwise set. Too large values can break some clients and
  cause other trouble.
- passwd-file userdb wasn't working
- PAM crashed with 64bit systems
- non-SSL inetd startup wasn't working
- If UID FETCH notices and skips an expunged message, don't return
  a NO reply. It's not needed and only makes clients give error
  messages.