Found in Bengal kittens only. Starting around 4 weeks old and lasting until the kitten is about 16-20 weeks old.  It's at it's worst around 7-13 weeks old, right about the time the kitten is ready to go home.  Bengal kittens begin to have longer "guard" hairs protruding from their coat.  In the wild Asian Leopard cubs have these guard hairs to help camouflage them from predators.  Many consider it a stage of being an "ugly duckling" where the Bengal is about to begin a great transformation.  The kitten looses contrast and its coat takes on a dull appearance. The undercoat becomes more prominent in the weeks to come and continues to change color(becoming more beautiful) until the cat is about a year old. 

Here's a picture of Safari at about 16 weeks old and then at a year old.

Great example below of one of our kittens in the fuzzy stage and then as an adult.