I'm not sure why it would change detected resolutions. I'd probably choose the resolution that gives you the best picture quality.
I might also bring this up with the service center in Algeria, and see if they can assist further.
I'll make it short. (escuse my english if...)
I bought my Samsung plasma PS42A450P1 in April of this year; and i had a problem with the picture, depending on the input the display was different.I called the service partner of samsung, present here in Algeria, and they came the next business day.
They called the problem "Black screen", and told me that they have to take the tv to their repair center.
The next day, they bring the tv repaired.
Until here, everything is fine, BUT what make me confused, is that before reparation, the native resolution detected by the nvidia graphic card of my pc was 1024x768 and now it's 1366x768.
I have to many questions to ask, but the main is what is the best resolution to use since the panel is natively a 1024x768.