Well, a simple test shows that if you leave the seed field empty in plugin properties, it will not be used. (basically no different from the system random)
If you enter seed value, all random functions will use this seed and generate the same numbers every time you run your game.
However, if you need to set the seed to a random value later in the game with events, don't set it to "", set it to some time expression (tickcount for example, or unixtime)