[mew-int 2784] Not receive imap header only on startup

Hi all~
I use IMAP account for default and I have set the config in ~/.mew.el .

  (setq mew-imap-header-only t)

But Mew receive the whole mail header and body when I start Mew(M-x mew).
Then in the %inbox, 's' can get the header only and 'C-us' get the entire mail. This's ok.

I remember that Mew can just fetch the header on startup in the early version
using the above configuratioin. Is that my fault or Mew's change?

My box is:
   Mew 6.3
   Emacs 23.1

Best regards.