ZDoom

You are getting confused.

ZDoom uses a large number of different RNGs, each one for a specific action. All this gets saved to a savegame so whenever you save/relead the state is the same.

Concerning Randy's objection, here's a very simple solution: Save the state anyway but when in single player mode and not recording/playing back any demo ignore it and use one generic global RNG for everything.

Don't demos use the original RNG though? Or was that changed (or am I getting out-right confused with something else)?

This is what makes it possible to record a demo from a savegame and have it playback reliably, though.

Let's better say an unnecessarily added feature for ZDoom.

Dunno, I don't see this as a bug so much as a missing feature. Not saving the RNG seed in single player should be a MAPINFO option. By default, saving the seed makes sense to me.

There's actually 2 problems here:

1. The seed is preserved
2. There's tons of different RNGs.

In Boom's single player mode only a single RNG is used and its state not saved. That makes things a lot more random.

I have noticed a number of times in the past that loading and reloading a save game can lead to the exact same supposedly random event over and over. I just assumed that things were meant to be that way as a result of, I dunno, some form of making demos or saves or whatever more reliable.