Captions change figures layout when plotly subfigures are used

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

I'm simply trying to render two plotly figures side-by-side on a website (using layout-ncol: 2), with a simple caption for each, but the captions change the layout. Each figure is created using make_subplots.

I think this issue might be related to #12839 (and maybe #7967)

Steps to reproduce

Render website using quarto render. Resulting _site is joined in a zip.

test-site.zip

Config: _quarto.yml

project:
  type: website
website:
  search: false
  title: "Test"
  page-navigation: true
  navbar:
    left:
      - href: index.qmd
        text: Home
      - about.qmd

format:
  html:
    toc: true

Main file: figs/test.qmd

---
title: "Minimal working example"
author: "rabyj"
format:
  html:
    code-fold: true
    toc: true
    self-contained: false
engine: jupyter
execute:
  echo: true
  warning: false
  eval: true
  error: false
---

Setup imports

```{python}
import numpy as np
import pandas as pd
import plotly.graph_objects as go
from plotly.subplots import make_subplots
```

Function

```{python}
#| label: test-function
import plotly.graph_objects as go
from plotly.subplots import make_subplots
import numpy as np

def create_minimal_example():
    """Minimal example showing subplot title positioning issue."""

    # Hardcoded data
    feature_sets = ["observed", "0blklst"]

    # Sample data for each feature set
    accuracy_data = {
        "observed": [0.95, 0.94, 0.96, 0.93, 0.97],
        "0blklst": [0.92, 0.91, 0.93, 0.90, 0.94],
    }

    f1_data = {
        "observed": [0.93, 0.92, 0.94, 0.91, 0.95],
        "0blklst": [0.90, 0.89, 0.91, 0.88, 0.92],
    }

    # Create subplot
    fig = make_subplots(
        rows=1,
        cols=2,
        shared_yaxes=False,
        subplot_titles=["Accuracy", "F1-score (macro)"],
    )

    # Add traces
    for feature_set in feature_sets:
        # Accuracy subplot
        fig.add_trace(
            go.Box(
                y=accuracy_data[feature_set],
                name=feature_set,
                boxmean=True,
                boxpoints="all",
                showlegend=False,
            ),
            row=1,
            col=1,
        )

        # F1-score subplot
        fig.add_trace(
            go.Box(
                y=f1_data[feature_set],
                name=feature_set,
                boxmean=True,
                boxpoints="all",
                showlegend=False,
            ),
            row=1,
            col=2,
        )

    # Update axes
    fig.update_xaxes(
        categoryorder="array",
        categoryarray=feature_sets,
    )

    return fig
```

Plotting no captions

```{python}
#| label: test-no-cap
#| layout-ncol: 2
fig1 = create_minimal_example()
fig2 = create_minimal_example()

fig1.show()
fig2.show()
```

Plotting with captions

```{python}
#| label: test-with-cap
#| layout-ncol: 2
#| cap-location: bottom
#| fig-cap:
#| - "test1-caption"
#| - "test2-caption"
fig1 = create_minimal_example()
fig2 = create_minimal_example()

fig1.show()
fig2.show()
```

Actual behavior

Captions are added next to the two figures, and the two figures take one column and two rows.

Expected behavior

Captions are added under each of the two figures, one for each column. Like this but with captions under.

Your environment

General env:

• IDE: vscode 1.103.2 (6f17636121051a53c88d3e605c491d22af2ba755)
• OS: Ubuntu 24.04.3 LTS (Linux x64 6.14.0-29-generic)

Python env:

• plotly: 5.22.0

Quarto check output

Quarto 1.8.23
[✓] Checking environment information...
      Quarto cache location: $HOME/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.3.1: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.8.23
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: 2023

[✓] Checking Chrome Headless....................OK
      Chrome:  (not detected)

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

[✓] Checking Python 3 installation....OK
      Version: 3.8.20
      Path: $HOME/Projects/envs/epiclass_py3.8/bin/python3
      Jupyter: 5.8.1
      Kernels: python3

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

[✓] Checking R installation...........(None)

      Unable to locate an installed version of R.
      Install R from https://cloud.r-project.org/

Start with figs/test.qmd and the _quarto.yml configuration, then run quarto render on the provided example. Compare the generated _site output for the test-no-cap and test-with-cap blocks; done means two plotly subfigures remain in one row with each caption below its corresponding figure.