AI cheating on single-player maps.

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R55Max

Perhaps this situation arose due to a map bug? Marmot, have you noticed such oddities on random maps?

No, I haven't encountered this on random maps, but I haven't played them much – I've mostly played standard single-player maps and custom ones. Fortunately, I've only encountered this on two maps (the other was the "Islands" map, a WoG map).
Here's what I wrote about that case:
http://wforum.heroes35.net/showthread.php?tid=772&pid=33018#pid33018
I looked at the map in the editor. There's no corresponding save file left, unfortunately. But I'm sure that: 1) the enemy was too weak to learn "Dimension Door"; 2) the guild of mages in his only Castle didn't have that spell; 3) there was no scroll with the spell or a book of air magic within reach of that hero.
Is a map bug when a spell or artifact appears even when it's forbidden by the author?

Added after 26 minutes
Here are a couple more threads that provide examples of AI cheating:
http://forum.df2.ru/index.php?showtopic=19126
etoprostoya:
I've already observed and described this bug, when the AI player gets spells like Town Portal or Dimension Door, even though it seems like there's no way for them to get it. Or teleports from Cursed Lands to their own town.
http://forum.df2.ru/index.php?showtopic=15443
read here:
Akorg:
On the seventh map, I was surprised by a bug (I don't know what else to call it) that allows the enemy to cast Town Portal from Cursed Lands.
etoprostoya:
This is a bug in the game and not the only one that appears in this Campaign. On the map where Armageddon's Blade is found, there's a bug where enemy heroes fly, even though they have neither the Flight spell nor Angel Wings.

Воскресайте, камінні душі, Розчиняйте серця і чоло, Щоб не сказали Про вас грядущі: їх на землі не було…
(Василь Симоненко. Люди – прекрасні)