Hi, good question. So what's going on is that there is another random number generator which is optimized for speed over quality for certain internal uses.
So to make it easier to set a random seed and not have to worry about which random number generator gets used where, I just pushed an update to ITensor that now includes a function "seedRNG(int)".
So you can just do: seedRNG(seed); and it will seed all of the random generators used throughout ITensor (just two of them at the moment).
If you want more details about the other one, I can tell you more about it, but it's only intended for certain cases where one wants sort of a "quick and dirty" random number generator (it's just a linear congruential generator).