It is a well known bug that the Enlightened Spirit's level 18 core enhancement "Celestial Spirit" deactivates upon death. It also deactivates upon equipping an item with the property "feather falling" (the spell itself or a clicky is not enough). This even happens if a warlock already has a "feather falling" item equipped. Maybe "feather falling" is one of the properties checked upon death/resurrection, and the two deactivation bugs share a common origin.

Hopefully that information helps developers track down the bug in any case.