How can the spacer be mounted backwards? It's just a tube? How would one know which way to install it if it is different?
Sure it's a tube, but it has a machined step on one end.
This will reach inside the bearings inner race, about half way trough, to meet with the flanged spacer on the left (sprocket) side.
Sure it will fit the other way round, bearings will fit fine... untill the wheel is mounted.
The right side flanged spacer will be forced against the stepped side of tube, and it will push the left bearing out again.
This will make the wheel look just like in your video.
Take the wheel off again, it will only take a slight effort to take the bearing out, since it's allready on its way. flip the tube, make sure the stepped side is on the cush drive side, reinstall the bearing.
please do not use locktite, or an extra spacer, no need for that, trust me.