A great thread I have used in the past for RND, RANDOM, etc is the following one: The limits of Rnd - General - Xojo Programming Forum
In your specific instance I think what you are getting is as expected. When you seed the class (at whatever instance you do it) the next call will use the same seed every time. The following paragraph I believe tries to explain this:
You might use this when you want to re-initialize a Random object but don’t want to create an entirely new one. If you are creating multiple sequences, this helps to make the sequences unrelated to one another.
In other words, the sequence after the call will always be the same (but you can keep making the seed call to generate new sequences). If you call the class without using the seed property/method you should get different results (i.e. not the same sequence every time you call it) - i.e. more so like the RND function.