`SortedSet` returns different results for equal indexes. about swift-collections HOT 3 OPEN

func test_indexOf() {
  var set = SortedSet<Int>()
      
  for i in 0..<50 {
    set.insert(i)
  }
  for (item, index) in zip(set, set.indices) {
      let i = set.index(of: item)!
      if i != index {
        print("Some issue with index(of:)")
        break
      }
  }
}

func test_indexForKey() {
  var sortedDict: SortedDictionary<Int, String> = [:]
  for i in 0..<50 {
    sortedDict[i] = "\(i)"
  }
  for (index, item) in zip(sortedDict.indices, sortedDict) {
    let i = sortedDict.index(forKey: item.key)!
    if i != index {
      print("Some issue with index(forKey:)")
      break
    } 
  }
}

func test_findAnyIndex() {
  var tree = _BTree<Int, String>()
  for (key, value) in (0..<50).map({ ($0, "\($0)") }) {
    tree.updateAnyValue(value, forKey: key)
  }
  for (index, item) in zip(tree.indices, tree) { 
    let i = tree.findAnyIndex(forKey: item.key)
    if i != index {
      print("Problems with findAnyIndex")
      break
    }
  }
}

extension _BTree {
  @inlinable
  internal func findAnyIndex(forKey key: Key) -> Index? {
    var (lo, hi) = (startIndex, endIndex)
    while lo < hi {
        let mid = index(lo, offsetBy: distance(from: lo, to: hi)/2)
        if self[mid].key < key {
            lo = index(after: mid)
        } else {
            hi = mid
        }
    }
    return lo < endIndex && self[lo].key == key ? lo : nil
  }
}