Technically, when you append() a RequestContext, you make it share the same internal state as the one you append to (and that's why you cannot append a RequestContext where you already create()d or edit()ed proxies, or invoked methods); so the order of invocations will be the exact order you made them in your code, whichever the RequestContext you used.
So, this is "guaranteed in practice", but I can't tell if this is "officially" guaranteed "by the API".