Lots of quarto_ipynb files created

[memeplex]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

When previewing qmd files a number of auxiliary quarto_ipynb files are created and left alongside the source document. This is the case even if keep-ipynb: false.

AFAICS this is a regression in 1.9.36 (I can't reproduce it in 1.8.27).

Steps to reproduce

Create test.qmd wih contents:

---
execute:
  keep-ipynb: false
---

```{python}
2 + 2
```

Then run quarto preview test.qmd.

Actual behavior

I get:

 test.html  test.qmd  test.quarto_ipynb  test.quarto_ipynb_1  test.quarto_ipynb_2

Expected behavior

Only test.html test.qmd with no clutter except when keep-ipynb: true.

Your environment

VSCode 1.113.0
macOS Tahoe

Quarto check output

❯ quarto check
Quarto 1.9.36
[✓] Checking environment information...
      Quarto cache location: /Users/carlos/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.8.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.4.5: OK
      Typst version 0.14.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.9.36
      Path: /Users/carlos/Desktop/quarto-test/.venv/lib/python3.13/site-packages/quarto_cli/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)
      Chrome Headless Shell: (not installed)
      VeraPDF: (not installed)

[✓] Checking LaTeX....................OK
      Tex:  (not detected)

[✓] Checking Chrome Headless....................OK
      Using: Chrome found on system
      Path: /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
      Source: MacOS known location

[✓] Checking basic markdown render....OK

[✓] Checking R installation...........OK
      Version: 4.5.2
      Path: /opt/homebrew/Cellar/r/4.5.2_1/lib/R
      LibPaths:
        - /Users/carlos/.rlib
        - /opt/homebrew/lib/R/4.5/site-library
        - /opt/homebrew/Cellar/r/4.5.2_1/lib/R/library
      knitr: 1.50
      rmarkdown: (None)

      The rmarkdown package is not available in this R installation.
      Install with install.packages("rmarkdown")

[✓] Checking Python 3 installation....OK
      Version: 3.13.5
      Path: /Users/carlos/Desktop/quarto-test/.venv/bin/python
      Jupyter: 5.9.1
      Kernels: ir, python3

[✓] Checking Jupyter engine render....OK

[✓] Checking Julia installation...