On any diet, you might hold weight for a while and then have a WHOOSh! where 2-3 pounds drop seemingly overnight. On a ketonic diet this seems to be the norm, rather than a rarity. When I participated in the low-carb newsgroup, people reported this all the time.
If you're building muscle and burning fat at the same time, your weight can indeed stay the same on the scales, but your clothes will be looser.