IMO its a flaw of the Ccell cartridge design that causes those bubbles. You want to draw oil in to the heating chamber to vaporize it, but the oil wants to run away from heat due to capillary action; which tends to result in those air bubbles. This is one of the reasons I've long felt the fully bathed wick of the Pax Era was superior to cartridge style atomizers.
Also make sure to do a "cool down" draw with Ccells and continue inhaling a while after you let off the button to clear the chimney of vapor and help cool down the tank.