Type Mismatch in wildcard (`_`) case in switch

IDE: Visual Studio X/Fire
Version: 10.0.0.2465 (develop
Target (If relevant): Island(OSX)
Description:
The compiler is wrongly emitting a Type Mismatch error for a _ pattern in a switch case.

Expected Behavior:
Compiles.
Actual Behavior:
See below.
Steps:

enum Tree {
    case Leaf(Int)
    case Branch(Int)
}

func testCase(a : Tree) {
    switch a { // W45 Switch does not cover all values
      case _: // E63 Type mismatch
        break
    }
}

Thanks, logged as bugs://83690

bugs://83690 got closed with status fixed.