Why choose a fragile solution when a robust one exists? Well, go ask the webmaster of United American Airlines.
I'm afraid several versions of Opera have struggled with the fragility of the <http://www.united.com/> flight lookup / order solution.
This is a bug in Opera. But sending notification about a loaded image only once and not once each time it is used is such a minor bug it would be an esoteric, low-priority report in the bug tracking system – if it wasn't for one single major site relying 100% on the opposite behaviour..
Morale: Webmasters and content management systems will never stop making things more complicated than they need to be.