Seems like the Map module is more finicky than the others. I have some photos selected in the filmstrip, that came from a Smart Collection. I did a search in the GPS address bar, and a yellow box with a dot was placed on the map at the found location. I right click on that box and select "Add GPS coordinates to selected photos" and nothing happens.
(If I drag all the selected images and let them go over the yellow box, that works, but I'm assuming that's not very precise and if later I drag more images to "near" that yellow box I won't get the same exact GPS location, which would not be good.)
I know I have successfully done this before with images that I selected via a Library filter, but this is the first time using images from a Smart Collection.
You neglected to say which version of LrC you are using. However, I've duplicated with just a selected image and not in a Smart Collection. In MAP, seach for a location. Search Result flag appears on the map Right-click the icon and select 'Add GPS Coordinates to Selected Photos' Nothing happens. Coordinates do not appear in the right hand panel. GPS icon does not appear on the photo. Drag the photo to the Search Result Flag and GPS coordinates appear in the right hand panel and GPS icon appears...
Be sure to include the first ten lines of the menu command Help > System Info. Provide all the details, rather than linking back to this thread -- experience shows that Adobe developers tend not to follow the links.
Also, note that the workaround of dragging photos from the filmstrip to the flag icon on the map won't necessarily assign the precise location of the search result. I first dragged a photo to a spot above the black dot in the icon, and then to a spot below the black dot, and even though the map showed a single flag with the number 2, the photos were assigned slightly different coordinates: