Bug? Insane invisibility duration

[Yermak]

Here is the situation:
While being in abyss, my TrFi got caught by Apocalypse Crab breath, that inflicted invisibility on him.
55910 | Depths:4 | Escaped the Abyss
56071 | Depths:2 | Gained mutation: You are very weak. (Str -4) [mutagenic glow]
56243 | Depths:3 | Gained mutation: Your vision is a little blurry. [mutagenic glow]
56307 | Zig:2 | Gained mutation: Armour fits poorly on your strangely shaped body. [mutagenic glow]
56404 | Zig:4 | Gained mutation: Your magical capacity is low (-10% MP). [mutagenic glow]
56494 | Zig:5 | Gained mutation: You are clumsy. (Dex -2) [mutagenic glow]
56614 | Zig:6 | Gained mutation: You have a pair of small horns on your head. [mutagenic glow]
56662 | Zig:7 | Gained mutation: You tend to lose your temper in combat. [mutagenic glow]
All this time rMut amulet was worn. And one scroll of vulnerability was read somewhere in the middle. And it is still not finished!
It seems to Me that such an incredible duration shouldn't be a thing.

P.S. I'm trying to source dive this now.

[Yermak]

On 700 turn mark it was somewhat funny to Me, because I thought it was just really long duration.
Now, when 2.6k turns passed, it's no longer that funny. I have this list of muts:

  Code:

You have a pair of small horns on your head.*
You have razor-sharp toenails.*
You have a somewhat thin skeletal structure (Dex +2, Stlth).
You have an uncontrollable temper.
Your vision is extremely blurry.
You are very clumsy. (Dex -4)
Your flesh is cold resistant.*
Armour fits poorly on your strangely shaped body.*
Your body is rapidly deteriorating.
You are very dopey. (Int -4)
You are a herbivore.
You are extremely frail (-30% HP).
Your magical capacity is extremely low (-30% MP).
You frequently scream uncontrollably.
Space frequently distorts in your vicinity.
You are very weak. (Str -4)

I'm herbivore, carrying only meat rations and starving.

P.S. Failed to find something in the code.

[Amnesiac]

Maybe you stacked too much invisibility(if it stacks) from chaos? I would just read ?vuln if there is one somewhere.

[Yermak]

Maybe you stacked too much invisibility(if it stacks) from chaos? I would just read ?vuln if there is one somewhere.

Did that. Didn't help.
On the moment of death invisibility lasted for 4k turns.