Inconsistencies when using UnsafeMutablePointer with String or Character types

I'm currently trying to implement my own DynamicArray data type in Swift. To do so I'm using pointers a bit. As my root I'm using an UnsafeMutablePointer of a generic type T:

struct DynamicArray<T> {
    private var root: UnsafeMutablePointer<T> = nil
    private var capacity = 0 {
        didSet {
            //...
        }
    }

    //...

    init(capacity: Int) {
        root = UnsafeMutablePointer<T>.alloc(capacity)
        self.capacity = capacity
    }

    init(count: Int, repeatedValue: T) {
        self.init(capacity: count)

        for index in 0..<count {
            (root + index).memory = repeatedValue
        }
        self.count = count
}

    //...
}

Now as you can see I've also implemented a capacity property which tells me how much memory is currently allocated for root. Accordingly one can create an instance of DynamicArray using the init(capacity:) initializer, which allocates the appropriate amount of memory, and sets the capacity property.

But then I also implemented the init(count:repeatedValue:) initializer, which first allocates the needed memory using init(capacity: count). It then sets each segment in that part of memory to the repeatedValue.

When using the init(count:repeatedValue:) initializer with number types like Int, Double, or Float it works perfectly fine. Then using Character, or String though it crashes. It doesn't crash consistently though, but actually works sometimes, as can be seen here, by compiling a few times.

var a = DynamicArray<Character>(count: 5, repeatedValue: "A")
println(a.description) //prints [A, A, A, A, A]
//crashes most of the time

var b = DynamicArray<Int>(count: 5, repeatedValue: 1)
println(a.description) //prints [1, 1, 1, 1, 1]
//works consistently

Why is this happening? Does it have to do with String and Character holding values of different length?