In short notice I've had a few kills with bleeding/poison/deadfall traps that haven't granted me the kill. Or at least not the message "You landed the kill on bla bla bla".

<656/1102 565/600 1197/1213><fighting><outdoor><civilized><4 PM><26000tnlvl>
The rain ceases.
Leata bats vainly at the biting insects.
Leata's swarm of insects wounds her.
Leata continues to bleed from her wounds.
Leata's bleeding mauls her.
Leata has some small but disgusting cuts. (75% - 90%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl> You scan east.
***** Range 2 *****
An elf wanders through here.

Leata has some small but disgusting cuts. (75% - 90%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl> Leata narrows her eyes and glares in your direction.
Weaving through the Flow of Shadows, you avoid Leata's attack.
Completing the Flow of Shadows, you come back at Leata with an attack of your own!
Your venomous slash MUTILATES Leata!
A spider-shaped axe poisons Leata.
Leata looks very ill.
*** POISONED! ***
You parry Leata's searing light.
You understand Leata's favorite defensive postures, and see her weaknesses.
Your venomous slash mauls Leata.
Your venomous slash mauls Leata.
Leata is covered with bleeding wounds. (50% - 75%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
You dodge Leata's searing light.
You dodge Leata's searing light.
You parry Leata's searing light.
You develop awareness of Leata's vital points, to better land harsh blows.
Leata parries your venomous slash.
Leata parries your corrosive slice.
Your sense of calm dissipates.
Leata is covered with bleeding wounds. (50% - 75%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl> pinc
You drive your axes into both sides of Leata's body.
Your brutal attack EVISCERATES Leata!
Your brutal attack MUTILATES Leata!
Leata is covered with bleeding wounds. (50% - 75%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
You parry Leata's searing light.
You parry Leata's searing light.
The headdress of Galadriel flashes pure white!
Leata parries your venomous slash.
Your venomous slash devastates Leata!
Your venomous slash decimates Leata!
Leata is covered with bleeding wounds. (50% - 75%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
You parry Leata's searing light.
You parry Leata's searing light.
Your venomous slash maims Leata!
Your corrosive slice EVISCERATES Leata!
Your corrosive slice decimates Leata!
Your venomous slash devastates Leata!
Leata is gushing blood. (30% - 50%)

<675/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
Leata narrows her eyes and glares in your direction.
Leata calls upon holy justice to wrack your mind with guilt and remorse!
Leata's wave of remorse === TERRIFIES === you!
Leata is gushing blood. (30% - 50%)

<466/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
You parry Leata's searing light.
You parry Leata's searing light.
You now have a keen eye for Leata's movements, and can predict where she will go.
Your venomous slash MUTILATES Leata!
Your corrosive slice maims Leata!
Your venomous slash maims Leata!
Your corrosive slice mauls Leata.
Leata is writhing in agony. (15% - 30%)

<466/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl> disem

Leata closes her eyes with a look of concentration for a moment.
You attempt a sweeping gut shot, but miss entirely!
Your disembowelment misses Leata.
Leata is writhing in agony. (15% - 30%)

<466/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
You dodge Leata's searing light.
You dodge Leata's searing light.
The headdress of Galadriel flashes pure white!
Your venomous slash maims Leata!
Your corrosive slice maims Leata!
Your venomous slash devastates Leata!
Leata parries your venomous slash.
Leata is convulsing on the ground. (0% - 15%)

<466/1102 587/600 1213/1213><fighting><outdoor><civilized><5 PM><26000tnlvl>
Leata's searing light MASSACRES you!
Along the Eastern Road


You flee from combat!

<400/1102 587/600 1212/1213><standing><outdoor><civilized><5 PM><26000tnlvl>
You hear someone's death cry.

Autosaving.
Your warcry has worn off.
*** WARCRY DOWN ***

<418/1102 600/600 1213/1213><standing><outdoor><civilized><6 PM><26000tnlvl> e
pinc Leata
Along the Eastern Road


An elf wanders through here.


This above is one example.

Or rather, probably not the bug you think.

Sometimes you get credit (in history, PBF, etc.) for kills even when you don't get the echo. IIRC, it's something to do with the victim not being in the room but I'd have to double check that. I do remember it looked annoying to fix and since people were in fact getting credit for the kills I didn't kill myself trying to fix it.

I'll make a note to take another look at this soon though. In the mean time, if you're pretty sure you should've gotten credit and know you did not (i.e., after the fact via PBF) please feel free to report that.