Collapsible blocks with "+" are not rendered as an open block

[chme]

Contribution guidelines

• I've read the contribution guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the problem doesn't occur with the mkdocs or readthedocs themes
• ... the problem persists when all overrides are removed, i.e. custom_dir, extra_javascript and extra_css
• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

Collapsible blocks (admonitions) with a + after the ??? token are not rendered as an open block.

Expected behaviour

Adding the + should render the block as open.

Actual behaviour

Block is rendered as closed

Steps to reproduce

You can see this behavior on the official documentation for mkdocs-material: https://squidfunk.github.io/mkdocs-material/reference/admonitions/#collapsible-blocks

The following block is not rendered as open:

???+ note

    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla et euismod
    nulla. Curabitur feugiat, tortor non consequat finibus, justo purus auctor
    massa, nec semper lorem quam in massa.

Package versions

• Python: 3.9.9
• MkDocs: 1.2.3
• Material: 8.0.4

Configuration

site_name: My Docs
theme:
  name: material

markdown_extensions:
  - admonition
  - pymdownx.details
  - pymdownx.superfences

System information

• Operating system: Linux (Solus OS)
• Browser: Firefox 94

[facelessuser]

I have confirmed this locally and this does indeed seem to be an issue with Mkdocs Material. Official docs seem to be afflicted as well: https://squidfunk.github.io/mkdocs-material/reference/admonitions/#collapsible-blocks.

[squidfunk]

Thanks for reporting. It's a regression because the print$ observable will now also emit on first subscription whether the page is in print mode or not. This led to open details elements always being rendered closed. Should be fixed with accfc4f.

[squidfunk]

Released as part of 8.0.5.