Video signal identification about TW9992

I'm currently testing TW9992.
I'd like to know how to handle the STANDARD SELECTION of 0x1c.
Is "current standard invoked" a value that always changes when the state changes?
I thought that N/A would be selected when I stopped the video input, but it kept the NTSC selection. Is this correct behavior?

By the way, the STANDARD selection is Auto detection.