When you spawn an item, by giving yourself one or using the /summon command, and in the same tick, but after it has spawned, teleport it, it will be teleported in the game but not visually, as it can be seen in the screenshots.

To reproduce it (screenshots show that as well):
1. Put two command blocks, the second one being 2 blocks on top of the first, with a block gap between both. This will make the bottom command block activate first than the top one when you power both of them at the same time.
2. In the bottom command block write the command "/summon Item (x,y,z coords)" and "/tp @e[type=Item] (new x,y,z coords)" on the top one. Put wooden or weighted pressure plates on the coordenates you set in the command blocks to see where the item will be.
3. Put a redstone block in the gap between the two command blocks, to activate both of them at once.

The item will appear on the location where you set it to spawn, but the pressure plate where you teleported it to will be the one triggered.