[mschnell]

That is actually a feature called ‚Stacks‘. Open the context menu on your desktop and de-select ‚use stacks‘.

[reddalo]

No, I know stacks and they're not them. In my case, new icons (e.g. downloads, files that I save, etc.) appear on top of each other, as if the desktop lost track of their position. It's clearly a bug that hasn't been fixed in a long time.