Started copies are kept for images in use

A server keeps an image's started copies (the ones a sandbox starts from in about half a second) while sandboxes are created from that image there. Once none has been for 2 days, the copies go. The first sandbox after that gap boots the image (a few seconds), and the ones after it start from copies again. Before, every image version kept its copies on every server it reached, used or not. See Images.