Just a note as I'm finding this kind of annoying too. from what I can tell I think how exp is calculated is based on no. of skills used before the kill.

so it may be something like:
base exp * (modifier based on how many different skill types were used since last kill, e.g. medical and combat.) * percentage of skills used of a certain type since last kill. (e.g. if you used 4 medical and 4 combat, you'd recieve identical exp in both, but double in combat if you only used 2 medical.)

anyway, i digress. as a temporary solution would it be possible to make kills always count the type of attack that killed them as a single hit? Obviously I don't know the code so the simultaneous nature of it may still interfere with giving exp correctly, but just thought it might be worth mentioning.

This is STILL happening in version 0.1.10
Particularly noticeable where there are dozens of hornets and Rock Golum Pegasi. You fight against and take down a Golum, with any attack that may kill two or more enemies, and hornet suddenly rushes in. You won't get the XP or drop from the golum. Instead you get the XP and 2 bits of the Hornet. If you kill two dragons, timber wolves etc., this is also a frequent occurrence. In fact, it is common for one of the enemies to vanish completely, as if it did not exist, and you get only one drop and XP reward.
the MOST ANNOYING thing about this is you ALWAYS get the LOWEST drop and XP.