Opera 12.12 on Windows stops sending events after forward/back navigation

[asnare]

While fixing issue #157 it was discovered that there seems to be a bug where events can sometimes stop working on Opera 12.12 on Windows 7.

Specifically, some of our tests on Sauce Labs for the page-view event that involve forward and back navigation fail. The circumstances seem to be:

If a page was left via forward/back navigation, when returning to via forward/back navigation signalled events will not be delivered.

Debugging shows that the Javascript is active and trying to send events, but for some reason the Image objects created never trigger an actual HTTP request. Consequently the onload and on error handlers never fire and the timeout fires. The event queue is eventually drained but no events seem to reach the collector.