Pages sometimes only partly load, always in multiples of 4096 bytes.

[JasperE]

I just moved a ready made CMSMS website from our testserver to our production server. All was fine before, but on the new server pages sometimes just stop loading in the middle of a file.
HTML files frequently are cut off after exactly 4096 bytes or a multiple of 4096 bytes. That means it can be cut off in the middle of html tags: "<a hre" and then nothing. Very weird.

Our previous php/mysql based CMS system was working fine, but on CMSMS it does give problems with output HTML that is pretty much the same. (I just rewrote the template file for CMSMS)
What's also weird is that in firefox the problem pertains after an F5 reload. If i then ctrl+f5 (ignore cache) the page loads fine, if i then hit a normal F5 again after that the page again partly loads. structural coincidence i guess

Versions:
Windows Server 2003
Microsoft-IIS/6.0
PHP Version 5.0.5
mySQL 4.1.7-nt

(I should note that unlike our production server, our testserver is a linux based system)

Does anybody have an idea about what might be causing the problems?

[JasperE]

I have moved CMSMS to a linux server, the problem is not showing up anymore.
I therefore suspect the problem was at at the IIS/PHP/mySQL end.