You found a bug. You think it's a really annoying bug. You reported the bug, including your opinion on the likelihood and the annoyance of having to do this really obnoxious workaround.
Then it got deferred. The official reason: "Not important enough to hold the release. Fix it for the next service pack."
Wait, what?! It's really annoying! Why on earth would you defer it?! It's time to go to the person making the decision and get an answer. You need to understand why they would make such a counterintuitive decision.
Lesson #1 in corporate politics: you are a tester. The person making the ultimate call is probably a director, VP, or someone else who's been around for a while and seen some things. They do not have to justify themselves to you. It doesn't matter if they've been promoted to the level of their incompetence; they still outrank you. Demanding justification will get you nowhere.
Your job is to make sure they understand the bug and its implications. They have to "get it". Once they understand, they can make a decision. If the person then wants to explain that decision to you, that's wonderful (and not uncommon), but it's not actually a required part of the process.
Seek confirmation of understanding, not justification.
Remember, you are an ally of and an advisor to the person making the release decision. You need to be someone they can trust, someone they want to see. If you're constantly asking for justification and making them defend their decisions, then you can't be an ally. So do what you really need to do - be an advisor and ensure understanding. Don't force your understanding of the ultimate decision; it'll generally come out anyway, and you won't have had to be obnoxious about it.