Update: This has been fixed!

Just in case others run into this issue, I wanted to document it here. @noescape causes some curious behavior when nesting closures. It appears to cause a captured mutable local to become a separate copy, meaning changes that should be visible in one sibling closure aren't visible to the other.

import Cocoa

func outerExecute(@noescape f: ()->Void) {
    f()
}
func innerExecute(f1: ()->Void, f2: ()->Void) {
    f1()
    f2()
}

func crashCity() -> NSString? {
    var local: NSString?
    outerExecute {
        innerExecute({ local = "Cool Beans" },
        {
            println("\(local!)")
        })
    }
    return local
}

crashCity()

If you remove @noescape this code prints "Cool Beans" as expected. If that attribute is present the second closure will crash with an unexpected nil.

Radar #20657776 filed. In the mean time you can just avoid @noescape