Preview Button Publishes/Updates Custom Fields

[Kevinlearynet]

Describe the bug
The "Preview" button inside of the Gutenberg editor will publish/update custom field values publicly, rather than isolate them to the draft preview.

To Reproduce
Steps to reproduce the behavior:

1. Change the value of a custom field for a published post
2. Click the "Preview" button
3. Open an Incognito window with the public post URL (not the preview URL)
4. You will see the new custom field value is publicly published

Expected behavior
When I click "Preview" changes to custom field values should only appear when the preview URL is viewed. The public, live post should not reflect these changes until the "Update" button is pressed.

Desktop:

• Mac Sierra 10.12.6
• Google Chrome 70.0.3538.102

Additional context

• Gutenberg Version 4.5.1
• This was originally filed as an issue with ACF, and upon further investigation with Elliot we determined that it is in fact a Gutenberg related issue: https://github.com/elliotcondon/acf/issues/730#issuecomment-442629260

[Soean]

Maybe it's a feature, not a bug? See: #11409
But I agree with you, thats not the behavior the user expects.

[Soean]

this alters the behavior for the preview button only and reintroduces the current (unfortunate) core behavior of saving metabox meta to the original post for previews. (see https://core.trac.wordpress.org/ticket/20299 -we can resolve this when we introduce meta revisioning to core)

source: #11409 (comment)

I think we can close this ticket as a duplicate?