Destructibles are considered enemies and trigger (at least some) on-kill effects

[Rihtorasti]

This was reported here: Destructibles Are Considered Enemies

and based on the responses in that thread is considered a bug. Destructibles can still be cursed and breaking them on my lich triggers the health drain from the blood pact talent, as well as life on kill from gear.

[Sarno]

Thank you for the report.

This is currently expected behaviour, but may be changed in future.