Required document link field for component property doesn't display error when touched but left empty

For an implementation project using component properties sidepanel (so: not using relevance):

• Open the channel manager and add a banner to the page.
• Open the banner's properties in the sidepanel.
• 'Touch' the Document field but leave it empty:
  • Tab to the Document field but move on without opening the picker or
  • Click on the field and then cancel the document picker 

Expected: error is shown that field is required

Actual: field appearance doesn't change