An easy way to prove this is to put a few wraps of tape about 1/4 of the way out one blade and the same length of tape on the other blade at the tip. My uneducated guess it that it's going to shake despite the fact that both blades weigh the same.

That being said I'd guess the single bladed props have the same "apparent" CG. in other words a heavier weight that is closer to the hub than the blade side.

What I'm trying to say is that the CG can be off as long as the weights of the blades are different to compensate. With both blades weighing the same the CG has to match on them.

I may be all wet here but just my thoughts on the matter.

Next time I go out I'll have to try some things.