Moved from Upper Deck - Econ

Due to fly out (for work) to MCO tomorrow and had selected a seat in the Upper Deck. A check last night, and the selection was still there, however this morning, I went on and found I had been moved to the lower deck.
I know its just a seat request at this stage, but I am wondering what event would have caused this - is it that folk with status get the chance to bump others ?
I've no problem with that, just curious, as last night, there were about 5 seats free in the upper deck, now its showing as all booked out.
Also, Have moved myself to be near the extra leg room seats, which are mostly empty at the moment - Is it frowned upon to move to them once we are airbourne ?
I know its just a seat request at this stage, but I am wondering what event would have caused this - is it that folk with status get the chance to bump others ?
I've no problem with that, just curious, as last night, there were about 5 seats free in the upper deck, now its showing as all booked out.
Also, Have moved myself to be near the extra leg room seats, which are mostly empty at the moment - Is it frowned upon to move to them once we are airbourne ?