Nev,
I expect that's OK as the charger's probably sensed that the battery is good and has dropped into maintenance mode where it pulse charges. I'm guessing that if you happen to check the voltage with your mulimeter in between pulses then of course the voltage will just be the same as the ordinary terminal voltage of the battery because the charger isn't actually doing anything at that time. I think that the Ctek starts a charging pulse when the battery's terminal voltage drops by around 5% so the interval between pulses when the charger is in this mode could be fairly long.
If the terminal voltage should drop to less than 12.9V the charger will sense this and begin a whole new fresh charge cycle.
In short, I reckon all is just fine and 'tikety boo' so sit back, relax, and enjoy the winter!!!
Cheers,
Steve.