Using the top containers "bulk operations" features where you can "update locations: multiple locations", if there's a long list of containers and you edit some number of locations, and then save, when you come back to do some other number of location edits that you didn't do before, the previous edits are removed. The new edits are saved.
So it's something like
Have long list of containers, select them all, "bulk operations" and then "update locations: multiple locations"
Assign some locations.
Do the same thing again to some other containers.
You just undid that first bunch you did.
I feel like this was hard to explain, hopefully that makes sense.