Mine post all the time. As mentioned about you always have to visit from the aeroplan site. If you happen to visit directly, or if you have multiple tabs open in your browser the cookies always seem to mess something up. (ie: you're already on ebay, open a new tab and go to Aeroplan).

I always close down the browser, go to Aeroplan, click ebay, bid and close down the browser. I typically use a bidding service, so I don't go back to rebid.

With other sites that use shopping carts, ie: Dell, Tiger Direct etc. you have to make sure you don't have anything in your cart BEFORE. If you were browsing Dell, had something in your cart and then went through Aeroplan you more than likely wouldn't get the points on anything already in your cart.