Ice in drinks.

Everyone knows ice floats because of some changes in the molecular structure that causes it to be less dense.

This works out great because, when ice floats in a cup of drink, it is supposed to set off a convection current, thus cooling the entire drink. (This is why air conditioners are placed high, and heaters, low.)

BUT. Ever had a drink like Milo? When you leave a cup of iced Milo untouched for 10mins or so, the top of the cup would be filled with water (much more transparent and without Milo particles). Logic indicates that the convection current would never have had this happening in the first place. What gives?

I thought of this while pouring myself a cup of Ice Cream Soda (had a little left, wanted to finish it) a while ago.

What I think is happening: Even though the water on top is indeed at a lower temperature, the water at the bottom is more dense due to having Milo particles in them, therefore no effective convection is occurring? ~_~