As I take a look into CController->loadPageStates(), there’s no code to load page states from GET method. I think it sounds confused to the users since they can set GET method to the form in CHtml::statefulForm(), but no way to get the states back. I don’t know if the dev team has a good reason why they don’t put this GET detection into the method.
I know this is NOT the bug. it’s mostly the issue, and I hope the framework should be able to do it without any overrides.
For people who needs to get the states using GET method, you can override the loadPageStates() then add your detection code into it.