[imp] Dimp : "headers already sent" errors in logs

[Emeric Jhelil]

Hi,
I am using horde-webmail-1.2.2 with dimp-1.1.1.

I meet these kind of errors in my apache logs (they appear by two).
- after login choosing dimp :
[Fri Apr 03 17:52:46 2009] [error] PHP Warning:  Cannot modify header 
information - headers already sent in Unknown on line 0, referer: 
http://test/imp/login.php
[Fri Apr 03 17:52:46 2009] [error] PHP Warning:  Cannot modify header 
information - headers already sent in Unknown on line 0, referer: 
http://test/imp/login.php
- in dimp, selecting options or compose
[Fri Apr 03 17:52:54 2009] [error] PHP Warning:  Cannot modify header 
information - headers already sent in Unknown on line 0, referer: 
http://test/dimp/
[Fri Apr 03 17:52:54 2009] [error] PHP Warning:  Cannot modify header 
information - headers already sent in Unknown on line 0, referer: 
http://test/dimp/

I have selected in my horde/config/conf.php : $conf['compress_pages'] = 
true;
And they disappear if it is set to false.

It seems to be linked to the flush function used in 
horde/dimp/lib/DIMP.php (header function) .
The errors don't occur if compress_pages is set to true and the flush is 
commented out.

Firebug shows these differences in the "GET dimp" http response header :
1) with flush and compress_pages = true :
Vary: Accept-Language
Transfer-Encoding: chunked
2) without flush and compress_pages = true :
Vary: Accept-Language,Accept-Encoding
Content-Encoding: gzip
Content-Length: 5155

Can it be resolved by a better configuration of my webmail ?
Are these missing header informations harmless ?
Is it better to comment out the flush function in 
horde/dimp/lib/DIMP.php or to let these warnings occur ?

Best regards
Emeric