I’ve been bitten by the draft auto-opening as well, but it’s worse than just getting the warning message. I’ve gone back to typing my post and then gotten the popup later, trying to direct me back to the other tab that has an older draft. At that point if I refresh the page I only get the older version of my draft, so in that sense this feature isn’t really preventing what it’s trying to prevent.
I’m not sure if it happens before you start typing. I just tried reproducing on meta, and it only happened when I started typing in the second tab. I tend to trigger this shortly after duplicating my tab to cross-reference what I’m writing. I lose track of which tab I started in, and when I start typing in the second tab by mistake the warning appears.
Would it be possible/reasonable to detect if another tab already has the composer open for the given topic and if so not open the composer for the new tab?