The body error message from proposal creation form is not displayed according to the text inside the field

[vsperiatu]

Describe the bug

When creating a proposal, the error message from the body input is not displayed according to the text inside the field. Also, this is happening only when rich text editor is activated.

To Reproduce

1. Log in as admin and activate the rich text editor (Organization settings -> Enable rich text editor for participants)
2. Visit the main site
3. Create a proposal
4. Complete the title input with valid text
5. Complete the body input with some text that is not starting with capital letter
6. Click on save
7. Delete the text from the body
8. Click on save again

Expected behavior

The error message should be displayed according to the text inside the input.

E.g. In this case, the text should be something like 'cannot be blank' instead of 'is using too many capital letters...' because the input box is empty

Screenshots

save_proposal_body_error.mp4

Stacktrace

No response

Extra data

Tested on nightly

Additional context

No response