I checked now. Spells are again chaotically ordered.

This bug was in R52 as well. It is almost impossible to duplicate this bug however as the spell list will randomly organize and disorganize itself as you play.

Also when i load a save file the list always begins organized so providing a save file with the bug in effect is impossible...

I played r52 onlt for 30 minutes so I can't confirm that. In r51 everything was ok.

I can reproduce this. I learned fire bolt, frost bolt, lightning ball, farsight and lightning bolt in that order. My spell list is ordered:
Lightning bolt
Fire bolt
Frost bolt
Far Sight
Lightning Ball

Which is the same order they appear in my identified items list.

This is easily reproduced with any elementalist learning Fireball. Your Burning Hands spell moves from letter A to letter D without warning.

Works for me. My guess is that we fixed this with some other bug fix during R54 development. I now have tried all permutations I could think of and all of them seem to work :-(

The problem still exists (r55). But I harvested know more information about that. This time when the spell order changed I heard that in-game music levels reseted themselves too 100 and 100. Maybe it's connected somehow?

I still need a description of how to safely reproduce it because I just can't. Could it be related to playing several games in a row or saving games and then restoring others? I yet have to see it once in the latest versions...

I still don't have an idea how to reproduce it... It happens randomly... :( But I will try to catch the moment of next chaotic spell randomization act ;)

I just found the bug in R55.
Orc wizard started with LB and Teleport. First spell book found in druid dungeon was Acid Bolt, learned in [C] slot.
I'm playing on steam. I've attached the save game.

I think I might got it! It happens probably every 1000 turns. My every new hero has a spell and music reset when cross the 1000 turn counter! :)

At turns 2000 nothing happened. Now I remember that it probably happens on the 1000th turn after going with new game or restoring the old one from saved game.

Wel... I saved on turn 2300 and started this save again. On 3000th nothing happened. On 4000 another bug appearing. I am still working with this. More researches tomorrow.

Further research: this happens every 1000 or 2000 turns. You can easily reproduce this with new spellcasting hero or one that was previously saved.

I concur, I just observed my spell list in the save game (L15 orc wizard now) scramble on turn 28000 precisely; there was also a brief pause between moves.

This problem was caused by feature 3413.

The list of spells is sorted once after a save game is loaded. The backup saves (which are created every 1000 turns) use the normal load/save routines which reset the spell order. In this case the spell list wasn't sorted after the save game was loaded.

Fixed.

I am so glad that I could find the bug :)