I don't think it's strange but is perhaps unusual. I think it indicates that your leptin and insulin weren't too mucked up when you started, i.e. your body is not resistant to burning fat and ketones as it's main source of fuel, as most bodies ravaged by the SAD are.
Are you very active? I think that can help.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.