Puzzling compiler error with Xcode 6.2 (6C101)

gistfile1.swift

// Works
class Testing {
    func something() {
        dispatch_async(dispatch_get_main_queue()) {
            [weak self] in
            if let blockSelf = self {
                blockSelf.somethingElse()
            }
        }
    }
    
    func somethingElse() {
    }
}

// Works
class TestingAgain {
    func something() {
        dispatch_async(dispatch_get_main_queue()) {
            [weak self] in
            self!.somethingElse()
        }
    }
    
    func somethingElse() {
    }
}

/* Fails with:
    error: cannot convert the expression's type '(dispatch_queue_t, () -> () -> $T3)' to type '()'
            self?.somethingElse()
            ~~~~~~^~~~~~~~~~~~~~~
*/
class TestingYetAgain {
    func something() {
        dispatch_async(dispatch_get_main_queue()) {
            [weak self] in
            self?.somethingElse()
        }
    }
    
    func somethingElse() {
    }
}