This document explains the procedure to display negative coordinates in OPIM. By default the extracted isometric doesn’t show the +ve or -ve symbol in the isometric coordinate label. But OPIM can be customize in a way that it can show the +ve or-ve signs as per the quadrant. Below is the images showing how coordinate label looks like by default.
If above problem still persists, then please create a Service Request and contact the Bentley Product Advantage group. Please include a list of all relevant details to get in depth analysis for a solution or workaround