Looks like the new google map plugin - cluster marker feature is not working perfectly.
It is nearly there ! Lets see if this can be replicated by the devs.
From max zoom out, to a zoom level in the middle, the cluster icon appears.
From the zoom level in the middle +1, in to full zoom in, the avatars and cluster icons all disappear.
PS: If this is good feedback, please send some rep points. (I need 200 points)