String の hasPrefix, hasSuffix の罠

Welcome to Apple Swift version 2.2 (swiftlang-703.0.18.1 clang-703.0.29). Type :help for assistance.
  1> "123".hasPrefix("123")
$R0: Bool = true
  2> "123".hasPrefix("12")
$R1: Bool = true
  3> "123".hasPrefix("1")
$R2: Bool = true
  4> "123".hasPrefix("")
$R3: Bool = false
  5> "123".hasSuffix("")
$R4: Bool = false
  6> "123".hasSuffix("3")
$R5: Bool = true
  7> "123".hasSuffix("23")
$R6: Bool = true
  8> "123".hasSuffix("123")
$R7: Bool = true

これ絶対おかしいだろ……