Preview Insert Page From File problem

I was just trying to combine two single-page PDFs into a single two-page PDF. This is something I have accomplished many times prior to Catalina. I was doing so by:

1. Opening one PDF in Preview (I'll call it Document #1)
2. Selecting Edit -> Insert -> Page From File...
3. Choosing the second PDF, with annotations (I'll call it Annotated PDF)
4. Dragging & dropping the inserted page to the beginning of the document using the sidebar.

This portion still appears to work. Preview shows in the title bar "Document #1 (page 1 of 2) - Edited". I then select File -> Save. The title bar shows "Document #1 (Page 1 of 2)".

However the issues:

1. The annotations in Annotated PDF were not included in the process.
2. I close the document. Then open the document. There is only 1 page.

To solve issue #1, I first exported Annotated PDF as a PNG. Important a PNG brought the annotations as well.

To solve issue #2, instead of using File -> Save, I instead used File -> Export as PDF... and called the new file "Document #1 Final".

Now here is the real kicker. To verify the steps I used and the issues I noticed, I attempted to duplicate the result. I started that process by copying all the relevant documents (Document #1 and Annotated PDF) to a new folder. When I opened up Document #1, it had three pages. Somehow the process had inserted Annotated PDF twice. Neither copy included the annotations.

So I started over again with two brand new pdf documents. I followed the same steps again. Again, Preview shows me a single page document until I move it to another folder. Then it has three pages, even though I only used "Insert from File" once.

So I ran the test again. This time I did not move the page after inserting. I just inserted and saved. Result: two pages, no annotations.

I then moved the page within the document & saved. It worked fine.

So one more time I tried the entire process from scratch:

open, insert, move page, save... result: 3 pages.

After the second test, closing & opening the file again correctly displayed the document. Whatever apparent (cacheing?) issue there was has disappeared during my testing. The issues I can still replicate are:

1. Using Edit -> Insert -> Page from File... followed by dragging & dropping the page before saving, duplicates the page instead of moving it. Until you close the document, however, Preview says it has 2 pages. Only upon re-opening the file does the 3rd page appear.
2. Using Edit -> Insert -> Page from File... does not ever include annotations added to the inserted page. Maybe a bug? Maybe a "feature"?