Has anyone found "problems" with NW's EUA (elite upgrade automation) process in terms of putting you in a window or aisle seat?

My profile has always said I prefer window seats. Everytime I fly NW, it's always a connecting flight as I don't have a reason to be in MSP/DTW/MEM.

When I'm upgraded...90% of the time, one of the flights is upgraded to an aisle and one is upgraded to a window seat. Any idea why this happens? I always have to call NW and ask them to change one of the flights.

I've also written them emails about their process and they can't give me clear answers on why this happens.

Does this happen to anyone else?

Thanks,
Rob