Apparently, this wasn't enough to fix it in all WMs. It's simpler to just use the same sequence as normal fullscreen windows and avoid headaches with virtual desktops, and Béla reported it working as well (I couldn't reproduce it, but nothing broke for me, at least).
I know the whole NtUserGetPrimaryMonitorRect thing is wrong and only works for one monitor, but that was already the case before, so I kept it the same since it won't fix a regression and we're in code freeze.