This is a side effect of the .messageContent element being overflow: hidden'd, which was done in a relatively recent version (1.3 maybe?) in order to ensure containment of the message when floats were involved (both in the message and with the advertisements commonly added) The extra block formatting context prevents the individual lines from wrapping around the new indicator.
It happens on the desktop and it isn't really fixable with a small tweak like may be possible on mobile as there's no vertical space to shift it up. Interestingly, shifting it up in mobile via Chrome's dev tools doesn't actually fix it; it visually moves but appears to leave some sort of "shadow" margin that prevents it from rendering as I'd expect; FF does shift it. That said, shifting it up does also run it over top of any user banners which may appear (it's basically butted up against them with the default positioning).
So as it stands, I don't see a reasonable workaround without completely changing where the new icon is displayed or creating other (probably more significant) inconsistencies. This will stay for the time being.