Just finished Premonition of Angron in Challenge mode - solo using Quake2 3.24 engine. Exit is via the Spaceship in Map 1 after killing Makron.
However, instead of going back to World server startmap, it put me onto Map 1 (Outer base) of quake2. What was interesting was I had all weapons + leftover shield and armour from playing POA. Shells - 200, Bullets -300 and so forth.
This must be a bug???.
Pity it did'nt give me added Andrei monsters.
Here is the log.
30/03/2015
1 h [Sol] has logged in using unreferenced engine
1 h [sol] create a game for up to 4 players
1 h [sol] Sol enters StartMap
1 h [sol] Sol enters Premonition of Angron
1 h [sol] Sol enters Power installation
1 h [sol] Sol enters Palace of Angron
36 min [Sol] has slain Makron
17 min [sol] Sol enters Outer Base
11 min [sol] Sol enters Installation
3 min [sol] Sol enters Comm Center
3 min [sol] stops his server
3 min [sol] Sol enters StartMap
2 min [sol] stops his server

Just one more thing. Picked up this head thingy in POA and it said "bring the head back to base"???. Does anyone know what to do with the head?.
Maybe that big Tank Commander guy lying on the table without a head - not far from Makron. Hmm have to did it again and see what happens.

A lot of custom maps (like POA) return you to base1 (aka Outer Base) after finishing them. There shouldn't be any difference in its gameplay.

Related to the message, I think that was related to the story behind the map. (perhaps you return back to the human 'base' with the plane once you finish POA?)