When allowing and configuring pop-ups for a layer, it should be an option to sort the windows based on an attribute value.
E.g. if the certain service-layer contains a Year-attribute, it should be able to see 2015 in the first window, and the year before last in the next window and so on. In the current version the sorting is not consistent, and so records from 2008 might be visual before 2014 records.
I has no effect to load the services as seperate layers and changing the drawing order - the same records are "on top"/in the first popup window.