I don't think downgrading is possible if you're not some kind of elevated user unfortunately. To get the call, I went through the standard support routine of IM-ing an assistant from the support website, who then transferred me over to a technical specialist who ended up scheduling a call with me and member of the Irish support desk. I went through everything again, and apparently after my support person consulted with their local engineering team, it was messaged back that the exhibited behaviour was 'expected'. I respectfully disagreed with the evaluation, but was told that I could not have this issue elevated as a defect. Instead, I was instructed to fill in the feedback form found here: https://www.apple.com/feedback/iphone.html
I filled it in as a bug report against iOS. You can decide how you want to approach this; I would fill out the bug-report form either way but the issue may end up with more gravitas if you too go down the route of talking to someone. I found a guy on Twitter who is having the exact same issue too (I won't put his username here), but assuming he is not one of the other respondents in this thread, there are at least 4 of us.