If you, for instance, create the following script for a level:

void onPlayer(jjPLAYER@ player) {
	if (player.charCurr != CHAR::FROG) {
		player.morphTo(CHAR::FROG, false);
	}
}

Then, while the player does correctly morph into a frog, the morphing animation still plays, despite the boolean flag at the end, for morph effect, being false. The same is true when the flag is set to true.

The current behavior is not technically incorrect, in that the flag only disables the effect that makes a bunch of glowing explosions appear around you when you morph, and that effect never happens when you morph into a frog anyway. But since there's no way to disable the extended frog morphing animation, I agree with you that the otherwise-unused flag should extend to that too.

Fix will be available in 5.8.