[imp] Unable to view / forward / send messages in certain charsets

[John R MacMillan]

I'm having a problem with IMP 4.0.4 / Horde 3.0.9 running on FreeBSD 
6.0 and charsets other than ISO-8859-1, US-ASCII or UTF-8.

If I try to view such a message, I get a completely blank page. If I 
attemt to forward or compose such a message, when I hit Send Message, 
the window goes blank and the message is never sent.

In both cases, the browser shows no page source at all.

In no case does an error show up in the logs with the settings for both 
PHP and Horde at E_ALL & ~E_NOTICE. If I enable E_NOTICE, I only see 
some notices about "Only variable references should be returned by 
reference" (I'm using PHP5), but I get those for messages that display 
normally as well.

I don't think it's a browser problem; it happens across multiple 
browsers (Firefox, IE, Konqueror) on multiple OSes (Linux, Windows).

According to test.php, I have iconv support, and I can use the 
command-line iconv to convert among charsets fine.

I've looked at other "Blank Page" bugs / mailing list postings, but 
they seem to be unrelated (I may have missed some; there are a ton of 
them, but they mostly involve blank pages on login or for certain 
features, and my problem seems specific to messages with odd charsets). 
I also found a Chorus bug listed about FreeBSD charsets that looked 
slightly promising (http://bugs.horde.org/ticket/?id=984) but the 
workaround did not help.

There's another weird twist I can't really explain: If I edit the 
mailbox manually to change the charset, I can view the message. If I 
then edit it _back_ to the original (and verify with diff that the 
whole mailbox is as it was), I can _still_ read the message. My only 
guess for that is that something gets cached when it works.

Any suggestions, or debug I can turn on to help diagnose?

Thanks,
John