Nice catch, thanks for pointing this out. I've updated the cache initialization to use `len(targetChars)` rather than `len(target)`:

    cache := make([]int, len(targetChars)+1)
    for i := 0; i < len(targetChars)+1; i++ {
        cache[i] = i
    }

AFAIK this makes them equivalent (fingers crossed). It seems to not have made much of a difference (-0.03s)