Starting with version 2010r1, ProSelect allows you to re-arrange the order that items are displayed in the Place Order window and this is carried through to the Order Report.

When you add items to an order they are automatically added AFTER the last order item of the same type. For example, a new print order will be added after the last print order in the list rather than next to the same image name or layout name.

When you print the Order Report,  multiple orders for the same image will ONLY be grouped together next to the same thumbnail image IF  the image numbers are listed consecutively. If they are not, then you may find the same Thumbnail image shown more than once on the Order Report. 

To prevent this from happening just click the top of the Images column in the Place Order window (click on the "Image No." heading) to sort your ordered items by image name and order type. (If you do this  with the Alt/Option key down it will sort by name regardless across all types.)