blinking showing channel

[emerald danjon]

Hi all.
Always i build a cable for X68000 and use on the LCD TV,have a random blinking,TV show again the Channel "PC",
in some moments is really funny avoid Bullets ,
is not a great problem and is not present when i use a PC monitor...,but i have curiosity ¿is this normal? any way for Fix?
thanks in advance and sweet dreams.