Electronic – Orcad Schematic Capture. Instances vs Occurrences

Using Orcad capture to create a multi-page hierarchical schematic I used the "Annotate…" option to renumber all parts. First set the them to "?" then incrementally update them.

However, after this when looking at part properties I realized that every single part in the schematic (not just the ones in the hierarchical pages) now had two different versions: the instance in white, and the occurrence in yellow.

Now every single change had to be done to both versions of the part, or I had to make sure that the corresponding occurrence field was deleted, so that it would default to the instance. You can see an example here:

In this case the part reference is different for the instance and the occurrence, while the PCB footprint in the occurrence is defaulting to the one in the instance.

This became very cumbersome and confusing very quickly. For example, copying a part and pasting it elsewhere, would generate a copy of the instance, not of the specific occurrence I was copying.

After many repetitions of "Annotate…" with different settings (and multiple errors while trying to generate a BOM) I found out that by going to every single occurrence and deleting the part reference field by hand, in most cases I could remove the occurrence, making cleanup easier. But I still had to fix a few more issues so that I could get a clean BOM.

My questions are:

1. What is the purpose of the "Occurrence" in non-hierarchical portions of the design?
2. How can I clean up these occurrences in the future, or how can I avoid them from reappearing?

Update: I am not sure why, but I again have undesired occurrences messing up part numbering. So I have to do yet another pass through the Annotate and cleanup cycle.

Related question: Hierarchical designs in Orcad Capture