All image stabilisation (including that on Canon lenses) works in this fashion. So if you don't like its behaviour then IS/VC lenses are not for you regardless of who makes them.
Obviously, all lenses stabilizers need a bit of time to star working, but the VC of the lens I tried took way too long.
What's more, with faster shutter speeds (let's say over 1/60) if I leave the VC enabled I get less sharp images than if I keep it disabled, so I always have to check the shutter speed I'm using to decide whether to live the VC enabled or not. Way too annoying.
That's bizarre and I've never heard of anything like that except with tripods where you need to turn off IS with longer shutter speeds as IS/VC keeps moving the lens when it isn't required.
That's the other reason why I guess VC has something wrong in that sample.
Anyway, they already gave me another sample, I hope I'll be able to run some tests in the next few days. I'll post here my considerations about it. I really want this lens to be up to my expectations, a good 24-70/2.8 with image stabilization would be extremely useful, for me...