There exist specific combinations of effects that cause the Editor to throw validation error.

Steps to reproduce:
1. From the dashboard, start creating a new Article
2. In any RichText field enter some text
3. Apply following effects (in that order): bold, superscript
4. Try to save the draft

Result:

• Validation error appears: Validation of XML content failed: Error in 18:0: Element section has extra content: para
• Notification "An error occurred while saving the draft" is visible

Note:

• Applying the effects in reversed order (superscript, bold) works.
• Applying another pair: (bold, subscript) also does not work (but subscript, bold do)
• Pairs (subscript, superscript) and (superscript, subscript) are working.