ZDoom

No. These things need special preparation. They are not supposed to be spawned into the map by ACS.

does spawnspot not set these variables?

You can't spawn these things without preparing them by setting some internal variables. That's not a bug. They just don't work on their own.

Wouldn't that qualify it as a bug?

The heresiarch balls are most likely not a bug at all, but a result of the way the game is coded.

As for the rest of it I have no idea.

1. If you give HolySpirit a spawnid and use thing_projectile to create it, the game crashes. The only way I could fix this was to redefine the spawn state so that it has no action functions.

2. If you make a Heresiarch that is scaled and use spawnspot to create it, it has a few problems. Effects such as the balls above its head are not scaled or always there. It loses the ability to attack sometimes. When it [i]should[/i] attack, it freezes up until something shoots it. If it is created with summon or thing_spawn these problems are not present.

3. thing_deactivate() does not work unless +ISMONSTER is set.

4. Custom weapons that use a_light1 or a_light2 leave their extra light permanently unless a_light0 is used. This seems strange because the stock weapons don't use a_light0 and they don't have this behavior.