I would be very interested in hearing how this could happen. For fat to be gained / stored you need an excess of energy, an excess of insulin and an excess of blood glucose (which would result in your excess of insulin). When one is in ketosis, insulin is controlled and at very minimal levels. Glucagon is dominant - the two, insulin and glucagon cannot be dominant at the same time, it's one or the other. One promotes fat storing (insulin) and one promotes fat burning (glucagon). A diet rich in protein and fat will result in the hormone glucagon being present in larger quantities and insulin being 'squashed' - for lack of a more scientific term.

Yes, you can stall in Ketosis, but gain weight? It's not possible.

-Nat

Edited to add that while it is not possible to gain fat while in Ketosis, it is possible to gain muscle - in which instance gaining weight is possible

N