unreadable docx output with flextable in labeled chunk

[FlukeAndFeather]

Bug description

If I create a flextable in a chunk with a label and render to docx then I get an "unreadable content" error in Word. This might be a duplicate of #7151, I'm not sure.

Steps to reproduce

I created a repo with the minimal steps to produce the error: https://github.com/FlukeAndFeather/unreadabledocx. It has two Quarto documents. The one called "unreadabledocx.qmd" produces the error and the one called "readabledocx.qmd" does not. The only difference between the two is the R chunk in "unreadabledocx.qmd" has label and tbl-cap options set, and "readabledocx.qmd" does not.

Expected behavior

The docx output of unreadabledocx.qmd should open in Word without warnings or errors.

Actual behavior

When trying to open unreadabledocx.docx in Word I get an error saying "Word found unreadable content in unreadabledocx.docx."

Your environment

─ Session info ──────────────────────────────────
 setting  value
 version  R version 4.3.2 (2023-10-31)
 os       macOS Sonoma 14.4.1
 system   aarch64, darwin20
 ui       RStudio
 language (EN)
 collate  en_US.UTF-8
 ctype    en_US.UTF-8
 tz       America/Los_Angeles
 date     2024-06-07
 rstudio  2024.04.0+735 Chocolate Cosmos (desktop)
 pandoc   3.1.11 @ /Applications/RStudio.app/Contents/Resources/app/quarto/bin/tools/aarch64/ (via rmarkdown)

Quarto check output

Quarto 1.5.43
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.2.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.41.0: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.5.43
      Path: /Applications/quarto/bin

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

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /Users/frank/Library/TinyTeX/bin/universal-darwin
      Version: 2022

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

[✓] Checking Python 3 installation....OK
      Version: 3.12.2 (Conda)
      Path: /opt/miniconda3/bin/python
      Jupyter: 5.7.2
      Kernels: stickleback, python3

(\) Checking Jupyter engine render....2024-06-07 10:15:54,895 - traitlets - ERROR - Failed to run command:
['/Users/frank/opt/anaconda3/envs/stickleback/bin/python', '-m', 'ipykernel_launcher', '-f', '/private/var/folders/x2/pd2b41ls033f6_p4h4h37k880000gn/T/tmp3djqqofr.json']
    PATH='/opt/miniconda3/bin:/opt/miniconda3/condabin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/X11/bin:/Library/TeX/texbin:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/Applications/quarto/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/texbin:/Applications/RStudio.app/Contents/Resources/app/bin/postback:/opt/homebrew/Cellar/git/2.45.1/bin'
    with kwargs:
{'stdin': -1, 'stdout': None, 'stderr': None, 'cwd': '/var/folders/x2/pd2b41ls033f6_p4h4h37k880000gn/T/quarto-session694ea50de5a5c1d2/bbf7c1ab7719a007', 'start_new_session': True}

2024-06-07 10:15:54,896 - traitlets - ERROR - [Errno 2] No such file or directory: '/Users/frank/opt/anaconda3/envs/stickleback/bin/python'
Traceback (most recent call last):
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/manager.py", line 87, in wrapper
    out = await method(self, *args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/manager.py", line 439, in _async_start_kernel
    await self._async_launch_kernel(kernel_cmd, **kw)
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/manager.py", line 354, in _async_launch_kernel
    connection_info = await self.provisioner.launch_kernel(kernel_cmd, **kw)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/provisioning/local_provisioner.py", line 210, in launch_kernel
    self.process = launch_kernel(cmd, **scrubbed_kwargs)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/launcher.py", line 170, in launch_kernel
    raise ex
  File "/opt/miniconda3/lib/python3.12/site-packages/jupyter_client/launcher.py", line 155, in launch_kernel
    proc = Popen(cmd, **kwargs)  # noqa
           ^^^^^^^^^^^^^^^^^^^^
  File "/opt/miniconda3/lib/python3.12/subprocess.py", line 1026, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/opt/miniconda3/lib/python3.12/subprocess.py", line 1953, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: '/Users/frank/opt/anaconda3/envs/stickleback/bin/python'


[Errno 2] No such file or directory: '/Users/frank/opt/anaconda3/envs/stickleback/bin/python'
[✓] Checking Jupyter engine render....OK

[mcanouil]

Duplicate of #7321