IE7 not Caching CSS Image over SSL

Question

I'm using the WebDevHelper toolbar for Internet Explorer to troubleshoot HTTP requests/roundtrips on my SSL site and noticed that IE re-downloads my CSS :hover images every time they are triggered. This causes a huge amount of roundtrips.

How can I prevent this from happening?

Edit: All static content is served with cache-control: public, so images, javascript etc. are cached in Firefox and Chrome. This problem is IE specific.

Answer 1

Serve static content via http, sure, but don't do separate images for :hover states. Proper css image sprites should be used. It's just good practice all around, via https or http. There are tons of resources available for creating sprites. Supposedly SpriteMe, [ http://spriteme.org/ ] is an attempt to automate css image sprite creation.