I added a shop building to the map as an area. The shop has a post box hanging on one corner, so I selected that corner node and added the amenity=post_box tag. This box never showed up, even though roads added later did. I checked, and the tag was there, but it disappeared one day.
Is this a wrong way to do things - and if so, why? The corner and the postbox is at the same location, so using the same node seems logical. I later added a separate point of interest just to get the box onto the map - this worked.
Helge Hafting