Whenever I change the description or the title of an image (or probably when I click on "Apply" on the "admin: albums-Images" page) all cached images in that album are deleted.

I think this is a bug. Is there a way to prevent this from happening?

There is no link between the apply of album changes and the cache. Only if you click on the "purge cache" would this happen.

You should also look into your server error log.

I checked the error logs and there's not much in there, some mentions about a "closed keepalive connection", I'm not sure what that means.
I made a small screen movie that illustrates what's happening: http://vasilis.nl/images/refresh.mov
Any idea what could cause it? I tried disabling both SEO plugins but that doesn't help.

Weird indeed but I have no idea and can neither reproduce this locally with the current trunk nightly nor our own site using plain 1.4.2.2.

Does it matter if you enter anything before the "apply"? Is it really ONLY the images in that album?

There are only a few places where the clearCache function gets invoked: the crop_image plugin, the edit processing if image rotation has changed or if you click on the clear cache button (which is not on the image page.), and the overview page clear cache button.

So at this point the only speculation would be that Zenphoto thinks some image has changed its rotation.

I just found out that it doesn't happen on every album, it happens on some. I'll try to find out what the differences are between albums where it happens and the others.