Easy to reproduce. Your own troops destroy resources on the same turn you capture an outpost. See the following screenshot:

The troops to the left just captured that outpost on the right, and thus all the enemy resource nodes (already fully upgraded) became mine. However, when I moved my troops back to where they are in the screenshot, they walked over the Iron Mine and destroyed it, even though it was mine. This is the third time this has happened this game.

It appears that for the purposes of resource destruction their allegiance doesn't get set until after the turn ends, instead of immediately after the outpost is captured which is what should happen. This results in your troops destroying your own resource nodes on the turn they were captured.