shipyard horror unique essence in docks act 3 not dropping essences in mirage

steps to reproduce:

- find mirage in docks next to the unique essence
- kill essence (rewards 1 essence)
- enter mirage (essence now rewards shows two essences as rewards)
- kill essence

expected: essence drops 2 essences as described
actual: no essences droped by the unique monster in the mirage

reference: 3 631 146 980

I had selected "rare shields" wish