It should cache but doesn't

Hello,

I have plenty of cache space allocated but my dynamically loaded jpegs still reload when the same thumbnail is pressed.

I am using one MC to load the jpegs in. So a new jpeg replaces the old one but it should be in the cache ready to load quickly when it is needed.

It works on a PC - but not on a Mac running IE 5.

I have no anti-cache script - why does it not stay in cache??

Thanks for you help in advance.

Osc