[fetchmail]idle command not working

I'm trying to use the "idle" option with an imap connection to an MS
Exchange server (5.5), but after each poll fetchmail will send an "A0005
LOGOUT" and disconnects.  I do get a "will idle after poll" log message, so
it looks like fetchmail understands the server has this capability.  My rc
file:

=== .fetchmailrc:

poll xxxxx proto imap auth ntls
   user "xxxxx(_at_)xxxx" pass "xxxxx" is "xxx" here keep idle

===

I'm running version 6.2.5 on FreeBSD.  Any ideas?  Thanks,
Steve