After 0x40 has been set, the 0x2 flag can be set and the player can be damaged by the next part of the keyframe. But if 0x40 is not set, keyframe marker 4 (which triggers 0x2 to be set) will not cause 0x2 to be added and no damage will be done to the player.
The 0x40 flag is not used in the player's saber keyframes because it doesn't seem to be needed for players. Marker 4 can set the 0x2 flag again regardless.