[imp] Command stream end of file

[Myke Place]

Some users on our system cannot access large (~50 MB) mailboxes through
IMAP. uw-imap returns 'Command stream end of file, while reading
line...' and the mailbox is not displayed. However, it is displayed if
the user logs out and then back in. According the Mark Crispen from the
UW c-client team, this indicates that the client disconnected to the
IMAP server without saying goodbye.

What sorts of settings in IMP/Horde/PHP might affect this. Does anybody 
have any suggestions for resolving this problem? Relevent version 
information follows:

# Horde: 2.2.4
# IMP: 3.2.3 
# PHP Version: 4.3.3

>From php.ini

max_execution_time = 60
memory_limit = 40M

As always, I'm happy to post additional info and I appreciate any and 
all responses.

-mp