when importing a larger number of poi or tracks from another map application, the explore app creates a new collection named in German "unbenannte Gruppe". In English maybe unnamed group. When I want to add all the imported waypoints to an existing collection, my work-around is this. I delete the unnamed group. Then the waypoints are unorganized elements. For these unorganized elements exists a batch function which does not exist for elements in collections.
The batch function is a little hidden. In the three dot menus ... of an element (waypoint, track/route) you press 'ok' and then select them one by one. Or you select (on top) all of them. At the bottom you can choose adding to or delete.
Now to the problem, which is reproducible and only exists since 4.0. When you select all unorganized (and you see only the unorganized) the batch processing happens to ALL elements, not only to the unorganized. If you choose the waypoints, then all waypoints from all collections. If you choose tracks, then the tracks of all collections. If you choose both, then ALL elements. If you choose adding to a collection, you are lucky. Then the unorganized elements AND ALL other elements are added to the chosen collection. It takes some time to manually remove the many elements which are added by this software error the a collection.
I was unlucky. I chosen delete and ALL waypoints, courses and tracks were deleted. My database was empty. !!!
The batch processing works fine if you don't select all elements, but select them one by one.