Glycerin, glycerine, and glycerol are NOT sugar alcohols. They are three words for the same thing. They are a component of fat.

Stored body fat (triglycerides) are each a glycerol molecule with three saturated fatty acids attached to it.

This does NOT mean glycerol is a fat. Glycerol is closer to a carborhydrate. It has 4.32 calories which is more than the sugar alcohols contain. It doesn't cause digestive problems because our bodies are full of glycerol (stored in our fat). We are quite used to it.

In ketosis, fat is partially burned to form a ketone body. And the glycerin is released as fuel in ketosis.

The products of fat metabolism are fatty acids and glycerin. The glycerin is used as a fuel source and the fatty acids are broken down further into ketone bodies, which become the primary fuel of the body in the absence of glucose. Any excess ketones are not stored but are excreted in the urine. The production of ketones during fat metabolism is called ketosis.

So if you are in ketosis, consuming glycerin in protein bars is not going to take you out of ketosis. You are already producing a ton of glycerin from ketosis.

http://www.wilstar.net/lowcarb/chem.htm
http://www.sportsci.org/traintech/glycerol/rar.htm
http://www.maxsportsmag.com/columns/issue26/26c1.htm
http://www.mendosa.com/diabetes_update_24.htm