why might the pineapple on the bottom of the pineapple-upside-down-cake float into the batter? I have 2 pineapple upside down cakes.  for one, the pineapple stayed on the bottom and can be seen beautifully when turned out of the pan.  The other the fruit floated up into the batter and cannot be seen when turned out of the pan.
Why?
There are two reasons I can think of to cause this problem. If the batters were not mixed up in one batch one might have been a little too wet and given room for movement. Alternately, if they were baked together in the oven on different shelves the temperatures and the direct heat (top or bottom) could be different for each one.

Good luck on the next batch.