**Resposted previous question with subscribed account as requested. **
I'm testing 1.3.10 on Joomla 3.4.1.
I have a series of custom fields including 1 mandatory checkbox. When I submit the profile without a checkbox selected there is no frontend validation to prevent the submit, additionally when the submit is correctly rejected by the server all of the edits to the rest of the fields are lost.
I assume this is a bug and not designed behaviour.