Strange issue with WHEN-VALIDATE-ITEM - 12c

Hello,

I am facing a strange issue in WHEN-VALIDATE-ITEM.

1. A Database block with one item - we will call it email_address
2. A button part of the DB block - we will call it save.
3. On WHEN-VALIDATE-ITEM trigger for email_address column, I have following.

IF :BLOCK.EMAIL_ADDRESS IS NULL THEN
      MESSAGE('You must enter an email'); pause;
END IF;

Problem: This trigger is not executing above code.

I also have the same exact code under WHEN-BUTTON-PRESSED trigger for the button - Save. It is not working there either.

What's more? I also put the same code at KEY-DELREC trigger at EMAIL_ADDRESS item. It is not working there too!!!