Default custom text is considered to be an Expression / Field after save

If you add a default text for a varchar field, after pressing ok, you see the text with quotation marks.

After you press save, they are removed and it's considered to be an Expression / Field.

When you want to change something else it gives an error because the default text is now considered to be a Expression / Field.

My db engine is InnoDB, HeidiSQL 11.0.0.5926