PIE on HP5500 (PPC2003) refuses to use cache

As the title says, Pocket Internet Explorer on my HP5500 with Pocket PC 2003 simply refuses to use cached files instead of redownloading them for each and every page. I have checked so there's enough space for them, I've checked so they exist. Yet PIE still refuses to use them. At first I thought it might be a problem with the webserver, but now I've tried it on 3 different webservers including IIS and it still won't work.

I've searched the web for a solid week now, and still haven't found a solution, or even a hint to solving this. Any suggestions on solving this problem would be much appreciated.

// Kim Forsberg