>If I select "Go back one hour" (or any other time), and then click on the button to get new messages, I first see an empty page, as expected. But after a few seconds, the page reloads, and shows me thousands of "new" messages!

If I understand correctly, you use the Time warp option from the Dashboard. Then, you select to go back one hour. This would then give you some messages in the map of messages frame. I assume this is what you have. From that point, a little while after, if you click on the icon to get new messages, this is when the situation happens. Is that correct? Based on what you wrote, you seem to have found a relation between the two. Can you elaborate more or provide more information so I can collect more data and see from that point?