Wow, well I actually consider that a bug, because it is inconsistent with the rest of the assertions. This bug has lived undetected for about six or seven years, though. I'll fix it, but what you can do in the meantime is call .deep. That's what you'd do for == with Arrays, for example:
scala> Array(1, 2) == Array(1, 2)
res12: Boolean = false
scala> Array(1, 2).deep == Array(1, 2).deep
res13: Boolean = true
scala> assertResult(Array(1, 2)) { Array(1, 2) }
org.scalatest.exceptions.TestFailedException: Expected Array(1, 2), but got Array(1, 2)
...
scala> assertResult(Array(1, 2).deep) { Array(1, 2).deep }