There is currently a bug when you have both the Chilblains, and Endless Winter talents. The effect of the Endless Winter talent causes the Chains of Ice spell to cause Frost Fever, but if the disease is applied via Chains of Ice it does not cause the 50% run speed debuff from the talent Chilblains. Also when pestilence is used to spread the version of Frost Fever that doesn't cause Chilblains (the chains of ice version) it also does not cause the Chilblains effect.