Steps to reproduce:

1. Log in to back office.
2. Go to Content / Content structure.
3. Create a new Article content.
4. Add custom tag to field "Intro".
5. Publish Article.
6. Edit previously added Article.
7. Remove custom tag from field 'Intro'.
8. Publish Article.

Actual result:

See attachment.

User can add Article without filling out required field 'Intro'.

Expected result:

User have to fill out required field 'Intro' for Article to publish content.