Validation of XML content failed when changing block styles in List block and publish it.

Steps:
1. Create new content which contains RichText field, e.g. Article.
2. Add List block.
3. Open dropdown with block styles.
4. Click on Normal - style is changed to Paragraph.
5. Type some text.
6. Click Publish.

Actual result:
Cannot publish, validation message occurs, see attached screen.

Expected result:
Maybe block styles for List should be disabled if user cannot publish content with changed style. Or validation message could be more user-friendly.