[BUG] double negative incorrectly interpreted

[peterfigure]

given the code snippet:

 fun domain(): Option<Domain> {
        val parts = value.split("@") // no pattern matching in kotlin :((((
        return if (parts.size != 2)
            None
        else
            Some(Domain(parts[1]))
    }

results in the error:

e: /Users/peter/develop/x.kt: (69, 25): pre-condition `index within bounds` is not satisfied in `parts[1]`
  -> unsatisfiable constraint: `(1 >= 0) && (1 < (parts.size))`
  -> 
`1` bound to param `index` in `kotlin.collections.List.get` 
  -> in branch: value != null, !(parts.size != 2), cond50, parts != null
e: /Users/peter/develop/x.kt: (69, 25): pre-condition `index within bounds` is not satisfied in `parts[1]`
  -> unsatisfiable constraint: `(1 >= 0) && (1 < (parts.size))`
  -> 
`1` bound to param `index` in `kotlin.collections.List.get` 
  -> in branch: value != null, !(parts.size != 2), cond50, parts != null, Domain != null, parts != null

it looks like !(parts.size != 2) is not being correctly interpreted to prove that parts.size == 2