[horde] error when viewing a mail in imp

[Edward Burr]

I have:
    Red Hat 9.0
    httpd (apache) 2.0.40-21.1
    php 4.2.2-17
    pear 1.0.1 (from horde)
    Horde 2.2.3
    Imp 3.2.1

Overall this is working great. I have a plain-text email
that is 587k in size, and when I try to view it, horde
produces an error message, and then I cannot load any
horde page until I stop and restart the web server.
Here is the error message:
===========================================================
Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to 
allocate 2048620 bytes) in
/var/www/html/horde/horde-2.2.3/imp-3.2.1/lib/MIME/Viewer/text.php on 
line 94

Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to 
allocate 140 bytes) in Unknown on line 0
===========================================================
Why is horde trying to allocate 8 MB to display a 587k file?

Nothing about this is logged in the httpd logs, except the
access_log shows the request to view the message.

Nothing about this is logged in horde's log, even though I
have set $conf['log']['priority'] = LOG_DEBUG; in horde.php.

The system is not short on memory or drive space. There is 
nothing unusual about this message; it is plaing ASCII text.
Does anyone have any ideas why this might be happening?

Thanks,
Edward Burr