Active naloxone is very bad as it will clear the opiod receptors while also preventing the bupe (an opioid partial agonist) from attaching as well.
This is untrue but a bit later on it...
Any composition of buprenorphine and naloxone will cause absorption of both drugs, it doesn't matter if it's a sublingual or an intravenous route (even orally, here's another catch - bioavailability and efficiency of certain ROA are 2 different things, buprenorphine is said to have ~5% bioavailability orally, that's not true, the bioavailability is much much higher but it's metabolized right away in the gut; both buprenorphine and naloxone will be taken up from stomach quite good but they'll go through first-pass metabolism).
Anyway, one might take into account that a few drugs injected i.v. at the same time may have different lipophilicity and that could make one drug or another cross BBB faster and in higher quantity. Anyway, it's not a matter of concern here. Imagine you're on buprenorphine/naloxone for some time. Levels of buprenorphine is stable at some point in blood due to its long half-life; with naloxone's very short half-life levels of it in blood doesn't build up.
A simple trail explains it better than talk in theory. Buprenorphine is given at 4mg for 8 days (i.v.), for another 4 days 4mg of naloxone (i.v.) are added to buprenorphine (no change in subjective withdrawal feelings), then buprenorphine is stopped and for another 4 days naloxone (i.v.) is only given (change in subjective withdrawal feelings minimal, may be even placebo). After buprenorphine is cleared out of body, continuation of naloxone injections will mean true withdrawal (but actually naloxone won't have any impact on severing it, naloxone is also an antidote for loperamide overdoses - no whole system withdrawal begins).
Buprenorphine has a very high affinity to mu-opioid receptors. Naloxone is a good antidote for morphine-like drugs and synthetic opioids overdoses. But naloxone affinity is a lot lower than buprenorphine's. Buprenorphine easily forces naloxone out of mu-opioid receptors (I'm writing about mu receptors as they're crucial). A person with no tolerance is injected with 100mg of morphine HCl and overdoses, overdose is treated with 0.5-1.0mg of naloxone HCl, then 0.3mg of buprenorphine HCl is injected - it forces naloxone out of receptors.
Now my subjective view on using buprenorphine/naloxone preparations intravenously. I wouldn't inject even a solution of lab grade buprenorphine and naloxone both at once starting buprenorphine or buprenorphine/naloxone treatment. Some trials suggest that some amount of people feel some effects from naloxone (s.l. intake). Even if it's subjective I wouldn't risk as withdrawals have always been extremely hard for me, there were times I even went paranoid after 1 day. But I wouldn't fear injecting buprenorphine and naloxone both preceded by buprenorphine-only injection.
Anyway, as I believe buprenorphine s.l. bioavailability is at most 25% (source: UCSF Drug Dependence Research Center and The General Clinical Research Center). To feel alright I had to take minimum of 16mg of buprenorphine s.l. (not buprenorphine/naloxone!). This doesn't qualify me for Suboxone treatment, I guess. I wouldn't be given two 8mg/2mg tablets a day IMO. In such circumstances methadone has been found superior to buprenorphine (edited

).