Anyhow, splice is working just like push would work. It doesn’t throw an Error, but instead does as you say and converts the argument(s) to the Vector‘s type. Consider this:

var vec1:Vector.<int> = new Vector.<int>();
vec1.push(Vector.<Sprite>([new Sprite, new Sprite, new Sprite]));
trace(vec1.length, vec1);

That also outputs 1 0 because the pushed type (Vector.) converts to the integer 0. This is totally contrary to Adobe’s documentation, which states that an exception will be thrown.

You are also correct in that splice‘s third argument does not do as the documentation says as it doesn’t add the elements of the passed Vector, but rather converts like you showed. It’s not even a case of a type mismatch, as in your example, as this results in the same output as your example:

var vec1:Vector.<int> = new Vector.<int>();
vec1.splice(0, 0, Vector.<int>([100, 200, 300]));
trace(vec1.length, vec1);

In summary, Vector is still, as I stated in the article’s conclusion, type-safe. It just doesn’t behave as the documentation says it does and is therefore pretty strange to work with. Thanks for the insightful comments!

var vec1:Vector.<int> = new Vector.<int>();
var vec2:Vector.<Sprite> = Vector.<Sprite>([new Sprite, new Sprite, new Sprite]);
vec1.splice(0, 0, vec2);
trace(vec1.length, vec1);

What should this do? Throw an error? Attempt to add the Sprites to the vector? Attempt to add the other vector to the vector?

It kind-of does the last one. It will trace 1 0.

According to the documentation you pass in var args or a vector of objects to be spliced into it.
This is wrong. It takes var args, and nothing more, but it also does something weird. It converts everything to the type specified, even if it’s unrelated.