I bugged this in-game, a while ago but I thought I'd post some examples here.
When fighting creatures using a combination of backfire spell (Rhadams Curse or Scour Soul) and summoned beings (which is about the best thing I can get going), there is a good chance that I, or anyone in my group, won't receive experience from killing a creature.
This happens when:
1. The creature is cursed with a backfire spell.
2. The creature is actively engaged in melee with a summoned being (warriors, champs and golems).
3. The creature dies as a result of backfire damage resulting from damage inflicted on the summoned being.
It seems to happen mostly when they kill the summoned being in the blow, but that's not always true.
Here's some examples (happened with 2 out of 3 Goliaths this morning, the horror! ):
>A Draconian goliath rakes his claws at a skeletal champion and lands a colossal blow.
A skeletal champion shudders violently then collapses into a pile.
A Draconian goliath collapses with a final groan of defiance.
The Draconian goliath dropped 11 gold.
It also appears to have dropped a titanium strongbox.
>A Draconian goliath rakes his claws at a skeletal champion and lands an insanely-damaging strike.
A skeletal champion shudders violently then collapses into a pile.
A Draconian goliath collapses with a final groan of defiance.
The Draconian goliath dropped 25 gold.
It also appears to have dropped a brass strongbox.
Below, it kills the champ and itself and we do learn. The only difference here seems to be that it fell at Paez's feet?
>A Draconian sophisticate rakes his claws at a skeletal champion and lands a colossal blow.
A Draconian sophisticate collapses with a final groan of defiance.
The sophisticate slumps over dead at Paez's feet.
You gain 183 experience.
[You are able to absorb 183 points into your training experience pool.]
The Draconian sophisticate dropped 49 gold.
It also appears to have dropped a brass case.
The next one, the champ doesn't die, but I still don't learn.
>A Draconian warrior rakes his claws at a skeletal champion and lands a colossal blow.
A Draconian warrior collapses with a final groan of defiance.
It also appears to have dropped a clay box.
Thanks for your time!