ZDoom

[git=4770dc2dfbeaf8749589c4feedc104f26e5aaf6b]Fixed.[/git]

Yup, crashes for me too.

Does it crash for you if you did just TNT1 A 0 { } without anything inside of it? May be correlated.

It crashes for me.

Actor Test
{
	States
	{
	Spawn:
		TROO A 20
		TNT1 A 0
		{
			if( randompick(0,1) == 1 )
			{
				A_Log("jumping");
				return A_State("Skok");
			}
			A_Log("not jumping");
		}
		Stop
	Skok:
		VILE A 20
		Stop
	}
}

"Action list must end with a return statement" is the error message you will get if you define something like:
[code]Actor Test
{
States
{
Spawn:
TROO A 20
TNT1 A 0
{
if( randompick(0,1) == 1 )
{
A_Log("jumping");
return A_State("Skok");
}
A_Log("not jumping");
}
Stop
Skok:
VILE A 20
Stop
}
}[/code]
The problem is when you remove 'A_Log("not jumping");' then there is no error message and ZDoom starts up normally.
If you spawn this actor (again without A_Log("not jumping");) and the if condition is not met then ZDoom will crash.