When you run 2 fireplaces 1 usually will have better draft that the other. Since the stove is uaually the hotter running appliance it has better draft. The house needs to replace the air being sucked out of the house. This air will be replaced from cracks,leaky windows,water heater/furnace chimney,etc...This can cause serious problems mainly carbon monoxide being sucked back into the house,smoke from other chimney. Try cracking a window and see if it helps but remember a fireplace and stove can pull alot of air from a home. Good luck.