Omen of chance. Incorrect description or interaction?

Omen of chance description - "While this item is active in your inventory your next Orb of Chance will not destroy the Item".
From the description, it seems that the orb of chance won't destroy the item, but it doesn't guarantee you'll get a unique item. But...looks like it guarantee cause orb of chance has only 2 cases - destroy item or upgrade to unique. And with omen of chance we have only one option - upgrade to unique.
Does it wrong interaction between item or misleading description? If 2nd scenario then why we have omen of ancients with next description - "While this item is active in your inventory your next Orb of Chance will upgrade the Item to a random Unique of the same Item Class"? Why in first case with omen of chance description says what it will prevent item from being destroyed and in second case it will guarantee upgrade? Where is error?