Before mavericks, selecting several images in Finder and choosing Open on them would open them in Preview in one window, with all image thumbnails nicely on the left hand side bar. Since Mavericks, this is no longer the case. Sometimes the selected images all appear in one window, sometimes Preview arbitrarily open some images in one window and other images in another window... How can I force Preview to open all in one again?
Before reading zinne's answer, I avoided the problem by using Quick Look instead of Preview. It can be found in the context menu of selected images, between Make alias and Share, at least in my Maverics 10.9.5.