I will walk through exact cause of bug:
1: skin dead pig
2: gather lard
3: get option to gather lard a second time
4: attempt to gather lard again
5: pig instantly vanishes without leaving bones or anything behind
So from what it seems, the bug is having the gather lard option show up twice, when there is no lard remaining the game freaks out and disintegrates the pig when you click it.
I'm sure the bug plague will soon take another one of my beloved animals soon, so I will keep experimenting with all the options in different orders to see what happens.