[Dovecot] PERMANENTFLAGS response if ACL seen/write rights are missing

In dovecot 2.0.13, if a user does not have either s or w ACL rights on
a mailbox, PERMANENTFLAGS correctly indicates that the mailbox has not
permanent flags:

• OK [PERMANENTFLAGS ()] Read-only mailbox.

However, if one is set but not the other, the PERMANENTFLAGS list is
not being pruned appropriately. For example, for a mailbox with the
following flags:

• FLAGS (\Answered \Flagged \Deleted \Seen \Draft $Forwarded $Junk)

If s is set, but not w, I would expect PERMANENTFLAGS to look like:

• OK [PERMANENTFLAGS (\Seen)]

If w is set, but not s, I would expect this:

• OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Draft $Forwarded $Junk \*)]

However, in both cases I currently see all flags in the mailbox:

• OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft
  $Forwarded $Junk \*)]

michael