Remove operation does not work while using BoundsOctree

[ikpil]

The code is as follows.

        [Fact]
        public void TestNotWorkingRemove()
        {
            var octree = new BoundsOctree<OctreeItem>(600.0f, Vector3.Zero, 8.0f, 1.4f);

            var testCenters = ImmutableArray.Create(
                new Vector3(562.5165f, 0.0f, 942.26f),
                new Vector3(4511.894f, 0.0f, 3130.14f)
            );

            var items = new List<OctreeItem>();
            for (int i = 0; i < testCenters.Length; ++i)
            {
                var item = new OctreeItem();
                item.Idx = i;
                item.Bound = new BoundingBox(testCenters[i], Vector3.One);
                items.Add(item);
            }

            foreach (var item in items)
            {
                octree.Add(item, item.Bound);
            }

            foreach (var item in items)
            {
                bool removed = octree.Remove(item, item.Bound);
                removed.ShouldBeTrue(); // <-------------------------- why!?
            }
        }