The behaviour of the TV is such that when the TV restart or HD resolution on the external device is changed from 1080P to 1080i video format or visa versa, the 'native 1080' mode in the TV menu will be automatically reset to OFF.
If you wish to watch the original HD format in 1080P or 1080i mode after the resolution change or power reset, the 'native 1080' mode has to be manually set to ON.
Note: The 'Native 1080' option is only available in the TV menu when an external device with the 1080P or 1080i video format is connected to the TV through the HDMI or YPbPr input.