Mobs and items placed on the End Island portal do not appear in the overworld

When trying to send an item or mob from the End to the Overworld using the central portal on the End Island, the mob or item passes through the portal, but never appears on the other side. I have tested several mobs and items, in survival and creative mode, with one or more players. In no case have I been able to find the mob or item in the overworld.