Error after focus on Xinha field without entering text

Start with a clean document.
Click (focus) on the Xinha field.
Do NOT enter any text.
Click (focus) on a different field.
Save document.

Now you get an error
javax.jcr.nodetype.ConstraintViolationException: /content/documents/mydocument/mydocument/demonamespace:htmlfield: mandatory property

{http://www.onehippo.org/jcr/hippostd/nt/2.0}

content does not exist

If you do enter content or don't focus on the Xinha field, there's no exception.