ToME: the Tales of Maj'Eyal

Alright. I had a Level 7 Temporal warden at level 3 of Heart of the Gloom. I had the boss next to the stairs with my Warden on the stairs. I went back to the previous level, cast Precognition and activated the Regeneration rune. I went back to level 3 and attacked the boss over the 7 turns that Precognition lasts and didn't die to stop the spell early. When the timeline reverted back to normal There were now two bosses. A boss with full HP and a bosses that was almost dead. I went back to level 2 and rested cause I thought it was a graphical bug, but when I went back to level 3 I attacked and killed the second boss and got a lot of experience for killing it. I then killed the original boss and looked in my inventory and I had 4 artifacts, two of which were both the Summertide Phial.

TL;DR Made a copy of a boss with Precognition, got 2 of the same artifact.

Huh. I've used precognition a couple times and gotten similar effects, although often the copy has full health
This has lead to some problems when fighting bosses...

I also just froze an arrow that I fired permanently in time using Precog. I thought it was a quiver I could pick up, but when I stepped on it it said I hit myself.

Cheers!

Since this bug report seemingly didnt get enough attention, I'll bump it up a bit again.
All the issues presented here happened to me too in b42 - and did just cost me a very promising char when I tried to claim my personal fortress...
When I intended to fight the weirdling in the Shertul Fortress I used Precognition to check out what aces he has up his sleeves. After Precog ended, the boss was duplicated: one (the clone) few steps closer to me, where he was when Precog ended, the other (original) at the spot where he was when Precog was originally casted.
This produced some weird effects:
1. The clone was immobile. He didnt move but he seemed to cast. Not sure about the latter though since it was kinda hard to tell the difference which one does what.
2. After I killed the clone, his loot appeared where the original was when I casted Precognition in the first place.
3. After I killed the clone, the stairs disappeared - and left me in a pretty bad situation with most stuff on CD etc. while the original happily kept charging towards me (and finally killed me).

Major issue: Cloned actors
As stated above this can be a real gamebreaker. It happened to me already before with a cloned escort. However, there it didnt influence the game much, except for some useless immobile escort standing somewhere.
Funny enough, I managed to finish the escort as usual and got my reward. Somewhen later a "Quest failed" message popped up and it showed as failure in the questlog too. I checked if some random monster killed the immobile clone, but he was still alive. No idea why the quest failed - but it didnt matter at all for the game progress.

Mediocre issue: Cloned projectiles
Probably connected to the cloned actors as it seems similar - but much more reliable. Actually this one can be reproduced easily.
When you fire a projectile (e.g. an arrow) and it is still traveling when the Precog ends, the arrow will be "frozen" in time. Means, it just floats at exactly that position in the main timeline too.
This is not a gamebreaker, but kinda abusable since if someone (incl yourself) is walking on the floating arrow it will get full damage. Thus setting up arrow-traps is possible (or suiciding when not paying attention and thinking the arrow is just a graphics bug)...

Minor issue: Death messages in chat
Simple thing, not very important. If you die in the alternative timeline of Precognition, a death message is posted in the chat. Sometimes even the menu with "Restart new char/Char dump/etc" pops up in the background and the game saves/loads quite alot until you can actually continue playing in the real timeline again...
Annoying but nothing gamechanging though.

Dwarf temporal wardens run into Norgan clones and occasionally player clones. I auto-used Precognition and skipped turns to reproduce the bug.

Just encountered a similar bug in the ruins of kor'pul. I used precognition to scout out a vault and found several skelly mages inside. They all used manathrust on me and the precog ended, but it counted as death for my actual character. I got pulled into the void and after returning there was a clone of myself where i was standing when i used precog while my actual character returned adjacent to it. I took one step south and lost control of my character, the game started passing turns automatically and eventually the clone disappeared, which gave me control of my character again and made time pass normally. I haven't reopened the vault to check if the mages were cloned yet.