I'd talk to your vet, as this is something you will need to explore a bit more. It is definitely not normal and would seem to indicate some kind of discomfort. I have 2 dogs that do this, and both have syringomyelia, which is probably their reason for doing this, and unfortunately there is a very high rate of this neurological condition in the breed. But there could be many other things which would cause your dog to do this–for example, has your vet done a skin scrape for something like rabbit mites, as they tend to gather down near the rump and tail? another possibility could be something like disc disease, if there is some discomfort around those lower spine discs. It could have something to do with the hip joints. others may have some different suggestions–but if I had a dog doing this I would start with checking for other skin parasites, and then I would probably want to consider an x-ray, perhaps talking to an orthopedist, and also just familiarizing yourself with the various symptoms of syringomyelia to keep an eye out for anything else that might look suspicious. If there are other potential symptoms, I would consider seeing a neurologist as it can make a huge difference to get a diagnosis and to start managing this condition earlier rather than later–not least because you have the most options early on.
In other words–there is a really broad range of things that might cause this, but you will need to work through them with your vet and perhaps eventually, some specialists if your vet cannot pinpoint anything. Just as an aside, the dogs that I have had that have had problems with anal glands have never rubbed it against furniture. And for what it's worth, even when my Cavaliers have just had their anal glands expressed, they will still scoot. Scooting is really common in the breed and I suspect is due to some other level of discomfort then anal glands because I see it too often and to consistently when anal glands are clearly not the issue.
