PdfWriter add_page adds (re)writes old page instead of new

[DominiquePACCO]

Bug report

Bug description:

The purpose of the following code (as a simplification) is to add PDF pages alternatively from 2 different opencv images.
To make the sequence unique, a sequence number is written to each PDF page saved. The PDF is written every 2 images but this is not essential
Herewith I expect a resulting PDF file with 60 pages numbered #1, #2, #3, ... #59, #60.

However the resulting PDF file shows a sequence which in my case starts erratically from the 25th page:
#1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, #14, #15, #16, #17, #18, #19, #20, #21, #22, #23, #24, #20, #22, #18, #19, #29, #30.
#31, #32, #33, #34, #35, #36, #37, #38, #39, #40, #36, #37, #34, #35, #32, #33, #30, #31, #19, #29, #21, #18, #24, #20, #55, #23, #57, #23, #59, #20

#25, #26, #27, #28 are missing an have been substituted by #20, #21, #18, #19.
Then everything is back on track to #40
In the remainder of the sequence #55, #57 and #59 are on the right page. The rest shows an 'older' page

The import of PyPDF2 is version 3.0.1

pythonSeq.pdf

    os.remove("pythonSeq.pdf")

pdf_writer = PdfWriter()

image1 = cv2.imread("Picture1.png")
image2 = cv2.imread("Picture2.png")
for seq in range(1,61,2):
    clone = image1.copy()
    cv2.putText(clone,f'Seq#{seq}', (200,30), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 0, 0), 3)
    cv2.imwrite("python.jpg",clone)
    pdf_image = Image.open("python.jpg")
    pdf_image.save("python.pdf", format="PDF")
    image_reader = PdfReader("python.pdf")
    pdf_writer.add_page(image_reader.pages[0])

    clone = image2.copy()
    cv2.putText(clone,f'Seq#{seq+1}', (200,30), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 0, 0), 3)
    cv2.imwrite("python.jpg",clone)
    pdf_image = Image.open("python.jpg")
    pdf_image.save("python.pdf", format="PDF")
    image_reader = PdfReader("python.pdf")
    pdf_writer.add_page(image_reader.pages[0])

[pythonSeq.pdf](https://github.com/user-attachments/files/20565446/pythonSeq.pdf)

    with open("pythonSeq.pdf", "wb") as pdf_file:
        pdf_writer.write(pdf_file)```


### CPython versions tested on:

3.13

### Operating systems tested on:

Windows

[mdboom]

Is there a bug here in CPython itself, or is it more likely in one of the libraries you are using?

[DominiquePACCO]

It's likely a bug in the PyPDF2 package, in the PdfWriter module

[mdboom]

Thanks. I'm going to close this, then, and imagine you will have better luck filing this bug with that project.