When you install ReactOS onto a BTRFS volume and first log in you get an "unknown" device wizard which is actually a BTRFS device. Now, I have no clue if this is an issue with the BTRFS driver or if it's an issue with how we have it integrated in ReactoOS, but I really think that by using a built in driver we shouldn't be seeing an unknown device from it, at the very least I don't think we should have a popup when we login for it, so we likely should hide it.
I don't know if I really needed to get a log for this, but here's one. I just logged on. let the device wizard load with the unknown device, and then shut down the system. This was tested on Virtualbox, but I see the same thing happening on real HW.