I mean its normal for it to be slightly unstable. On your old firmware video its mostly hidden. On your video on the 0.76 firmware you can see more lines at the top and bottom. So the two videos do not show the same area of the signal.
Either your TV is changing the overscan somehow or the V.active, V.backporch values are different. You can try V.active 224 and check your TV zoom settings on 0.76 firmware.
Are you using linetriple on both firmwares?