(EDIT: I wrote the title when I thought the "problem" was related to GET form submissions - however, it seems to be far more general.)
I've just noticed that Opera does not display querystring parameters in the browsers address bar?! Do others see this? Is this a new thing? (Chrome and Firefox show the querystring like normal.)
The querystring is correctly processed - it is there. However, the URL in the address bar does not show the querystring until you move focus to it - at which point you then see the full URL. However, move focus away again and the URL parameters vanish.
I thought at first this was a problem with my HTML form (submitted via GET), but it seems to be any querystring params on any page!?
It's possible that you have a site that simply varies the querystring from page to page - in Opera it will look as if the URL is not changing.
I'm using Opera 17 (I seem to have been automagically updated from version 16 when I wasn't looking ?!)