Originally Posted by kumy
For now as a workaround, I've disabled EDIDs, and forced a modeline
Interesting finding, kumy.
Can you check what happens if you save the EDID from the "broken" TV (use nvidia-settings, go to the pane for the display, and click "Acquire EDID" to save a file) and force it on the "working" TV (use the CustomEDID X config option for this; e.g. 'Option "CustomEDID" "DFP-1:/path/to/edid.bin"' in the "Screen" section, obviously replacing DFP-1 with whatever your HDMI port is - see Appendix B of the README for more details)
The same experiment in reverse (supplying the "working" TV's EDID to the "broken" TV) would be interesting as we..