I've a Strato AG PowerWeb XE packet. Strato uses Apache/1.3.31 (Unix) and the following versions are installed:
PHP 3.0.18 : gd_lib: 1.6
PHP 4.4.3 : gd_lib: 2.0.28
PHP 5.1.4 : gb_lib: 2.0.28 (bundled compatible)
The following site shows more informations: http://www.tmq.de/info.php
I've uploaded 2 Testfiles on the bottom of my page that you can see the problem: http://www.tmq.de
(The files only content ASCII sings).
The problem persits on different computers and browers (I've tested Internet Explorer 6 and Firefox 2.0).