If a unit that has been affected by the Shadow Poison (Shadow Demon) is sent to limbo, while holding an Aegis of Immortal or having the skill Reincarnation (Skeleton King), that unit comes back to life without the Shadow Poison stacks. It should preserve the stacks.
No issues for actual Death.

Reproduction Steps:
  1. Get a Shadow Demon with Shadow Poison
  2. Create an enemy Skeleton King with Reincarnation
  3. Stack Shadow Poison upon the Skeleton King
  4. Kill him, preferably with Shadow Poison as the last blow
  5. Wait for the Skeleton King to come back to life

Current Result:

Skeleton King resurrects without the Shadow Poison stacks.

Expected Result:

If the Shadow Poison hasn't expired during the resurrection delay, the Skeleton King should come back to life with the Shadow Poison stacks, which can be incremented, released or auto-released when the duration ends.

Shadow Poison stacks has a 10 seconds of lifetime, which can easily overcome both resurrection durations. This is incredibly important for a possible huge nuke right after a resurrection.
Again, this is not an issue for the actual Death. Death should and is removing the Shadow Poison stacks.