Description

When you leave the Post Editor of content that contains a Spacer Block set to either Grow (previously Fill) or Fit, the browser will warn you about losing unsaved changes, even if you haven't changed anything. The issue does not impact Spacer Blocks that have a Fixed height.

Step-by-step reproduction instructions

1. Create a new Post.
2. Insert a Stack.
3. Insert a Spacer within the Stack.
4. Set it to Grow.
5. Publish.
6. Go back to your All Posts list.
7. Return to editing the Post.
8. Make no changes, but navigate away.
9. See that you were warned about unsaved changes (even though you didn't make any)

Screenshots, screen recording, code snippet

No response

Environment info

WordPress 6.6.2 and WordPress 6.7. Theme: Twenty Twenty Four (and others). No Gutenberg plugin.

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure