That's interesting. Very interesting.
I mean, if your IV'ing 100mg oxy or 8mg bupe in the first place, your very tolerant. And I don't think it's possible to be that tolerant without also being addicted. Granted, your addiciton may not be as bad as say, mine, because your "regular" dose is lower than 100mg oxy, meaning 100mg oxy gets you high. But 8mg suboxone IV is a shitload. it literally takes 24-40mg sublingual bupe to equal 8mg IV. So huge habit or not, it should have theoretically sent you into DT's. However, as Dhopeless stated, if you already take suboxone regularly, your receptors would be accustomed, and so it would be no problem.
Personally, I have only seen one person go into precipitated WD from bupe, and it went away a few minutes later because they injected more. It is very hard to go into DT's from bupe. You have to have a large addiction to full-agonists, and have to do bupe while your receptors are fully saturated. Remember, IV oxy only lasts an hour or 2 anyway.
So basically, by tje time you did it, half of the oxy IV was already out of your system, and so the bupe filling the receptors didn't cause DT's, since it's partial agonist activity is actually stronger than a small dose of IV oxy. You not having a large addiction plays a part, since obviously, however much you use on a daily basis, 8mg of bupe covers it, without shocking your system. In fact, it even got you high!!!
So no surprise really. People are just scared of bupe for no reason, even though I have banged oxy and dosed bupe shortly afterwards many times(I wait longer than an hour, but still)
(Edit to note that, again, 8mg IV bupe is A LOT. In fact it would take a good tolerance not to get sick...)