The wizard light will stay steady until the batteries are (nearly) charged. As far as I have been able to work out, it goes to steady, and the corresponding 14.4V output setpoint, when the battery voltage drops below some value, and stays there until it has been at or near the setpoint voltage for a few hours. It then cycles to the lower setpoint voltages and corresponding flashing light signals. The lowest of these does bump the output to the higher voltage for 15 minutes every 24 hours, what they call desulfation mode.
The actual output voltage may be less than the setpoint because of current and power limits, and generally will be when low batteries are receiving a charge.
In short, the converter is behaving as designed, from what you have written.
