Unless I'm missing a setting somewhere, objects created on a page will have the Y axis in relation to the page you are working on.
The exception is unclosed paths / shapes, including straight lines, created by the Pen Tool which seem to have their Y axis in relation to the origin of the very first page in a document.
This means that on p10 of my document the horizontal lines are showing an Y axis of 3044.8mm instead of 101.8mm!
Oddly if you convert a rectangle to paths and then remove two of the nodes to create a straight line you get the correct positioning.