Omen of Secret Compartments doesn't work properly

I found a Unique Jewelers Strongbox so bought an Omen for 9 exalts.
Activated it, opened the box and it used the omen but didn't let me open it again.

You owe me 9 exalts ¬_¬
(I'll take a unique Ventors box as I've not seen one in over 300 hours even though I'm specced fully into strongboxes with researchers. Take my gold please).