I have a RB1000 setup with a high speed 32gb CF web proxy card, web proxy works fine but when i go to a site with lots of pictures on it, sometimes it will not load all of them, if you refresh it others will show up but ones that were there go away. i think it might be a page issue because of the detected web browser is “Mikrotik HttpProxy” is there a way to change it to IE, Firefox, or Safari so that the page will be displayed properly?
that is certainly not the reason 
how did you detect what the server sees?
the problem must lie elsewhere. can you post a screenshot of an example page with this issue?