"Entity is not a player" when loading a saved game while being in multiplayer

[FreeSlave]

Load some map via console, quicksave the game. Then leave the game (e.g. via "disconnect" command). Then start multiplayer server via menu. Then press quickload.
I'm getting the fatal error

If I do the same thing on Half-Life (i.e. valve folder, with original libraries), the save is loaded without the error.

[SamVanheer]

The engine has special logic to reset maxplayers to 1 before loading entity data:

if ( !Q_stricmp(com_gamedir, "valve")
	|| !Q_stricmp(com_gamedir, "bshift")
	|| !Q_stricmp(com_gamedir, "gearbox") )
{
	svs.maxclients = 1;
	Cvar_SetValue("maxplayers", 1.0);
}

Mods don't get this treatment so the engine thinks the first maxplayers - 1 entities are players when they're actually something else.

There is no way to change the engine's behavior here so this can't be fixed.