ZDoom

Looks all correct to me.

So, what doesn't work here exactly? State switch can be avoided with [b]LOF_NOJUMP[/b] flag. See sound can be disabled with [b]LOF_NOSEESOUND[/b] flag.

Yeah, I noticed the SeeSound thing during my testing. I think you might want to create a new bug report for that, since it and the bug report in the OP are about two different things.

class ZombiemanTest : Zombieman replaces Zombieman
{
	States
	{
		Spawn:
		POSS AB 10
		{
			A_LookEx(LOF_NOJUMP,0,0,0,0,"See");//monster doesn't jump to the See state, but plays alert sound constantly.
		}
		Loop;

	}
}

Ok, after some further testing it seems like the jump to a specified state ("See" by default) is indeed averted, but I still think there is buggy behavior seeing as the alert sound is played as if the monster was alerted.

[code]
class ZombiemanTest : Zombieman replaces Zombieman
{
States
{
Spawn:
POSS AB 10
{
A_LookEx(LOF_NOJUMP,0,0,0,0,"See");//monster doesn't jump to the See state, but plays alert sound constantly.
}
Loop;

}
}
[/code]

I assume that the workaround is clear the default alertsound and play one manually via PlaySound() when the monster becomes alerted.

You might want to provide a runnable example which produces the problem, because in my tests the flag works fine.

Spawn:
		BATH BBCCDDEEDDCCBB 1
		{
			A_LookEx(LOF_NOJUMP, 0, 0, 0, 180, "See");
		}
		Loop;

		See:
		TNT1 A 0
		{
			A_Log("Chase");
		}
		BATH B 1 A_Chase;
                Loop;

Did anyone recently used A_LookEx with the LOF_NOJUMP flag successfully? Apparently, the flag is ignored and it always jumps to the monster's See state (no matter which State you provide, even "null").

[code]
Spawn:
BATH BBCCDDEEDDCCBB 1
{
A_LookEx(LOF_NOJUMP, 0, 0, 0, 180, "See");
}
Loop;

See:
TNT1 A 0
{
A_Log("Chase");
}
BATH B 1 A_Chase;
Loop;
[/code]