This sure sounds like it, and it is normal and they will not disable it. The workaround when you are at a stop and know you will need a fast start is to release the brake slowly until it starts to creep and press the brake lightly to stop. Now you are ready to launch.I'm also going to play with my braking to see if it is the hill braking thing. I know my driving has adjusted a bit to make slow starts from stops when I first start driving, but sometimes I have short trips where I don't really have to stop until I get into a left-hand turn lane and don't think about it. If it is that hill assist thing, I want them to disable it.
Hill hold only activates with a firm press on the brakes. So on stops where you only press lightly to stop, it will behave normally. That accounts for any variation in how it acts. It is completely repeatable in my car, and if you play with it at stops, I think it will be for you too. Then you can demonstrate it to the service department if you want (won't do any good).
Personally, I think it is unsafe as well. Before I figured out what was going on, I did another workaround: starting a half second or a full second before I would in a normal car. That's also scary and I don't do it anymore. And I've settled into hybrid style driving so occasions for a fast launch are seldom done by me anymore and this thread is the only time I think about it.