Ok, those that know me, know I just HAD to click on this just from the title!
Anyway, what you are describing has me thinking it is the anal glands expressing. They usually are expressed/emptied when they poop (if the poop if firm enough). I guess it is a marking/scent thing. Sometime dogs cannot empty the glands themselves and they end up getting backed up and it gets itchy, and causes them to to the "booty scoot" across you rug or furniture. Also not nice when guests are around.
If this is the case, I suppose the glands are expressing themselves. They do have a smell, kind of fishy, not very pleasant.
Also, I personally don't think Royal Canin is that good of a food, and they just raised their prices. There are much better options at lower prices.