This bug was found by TradeMrk, and we did some tests.
The Premise:
According to TradeMrk, he noticed that units in base would gain vet for no obvious reasons - particularly during blizzards. Since they weren't taking losses (they were in the HQ) and weren't fighting (in HQ), there was no obvious source for this XP. However, there was something getting kills: The Blizzard.
The setup:
What we did was very simple; we loaded up a winter map (Langreskaya Winter), and got into combat. After a unit got a single kill (1 squad member), the unit would then retreat to HQ. In this case, a gren squad firing on Russian engies.
(We tested this with multiple units - I just took pics of one case)
The unit that took the LOSS would stay on the field until the blizzard started getting kills.
At this point we waited for the blizzard to start killing guys; and we saw what we expected.
As you can see, the gren squad has gained the XP and a 'kill' for the combat engie dying - despite being in base.
And again:
What's interesting is that when the 4th squad member died, the gren WAS NOT awarded XP or a 'kill'.
By using multiple cases, we came to the conclusion (or logical correlation) that the grens (in this case) were awarded XP based on 'assists' - basically that the last squad to damage a MODEL was awarded the kill and XP.
We're fairly certain that this is a bug; cold 'kills' should be neutral, in that they are attributed to player-error, NOT actual PVP actions. In addition, more 'direct' (although still indirect) kills, such as mines, do NOT grant XP via the assist function - neither by getting kills directly, or by triggering a 'last-hit' scenario for the engineers that planted them.