Using Samsung Galaxy S3, running MCPE 11.1
After update I have a cow spawner without the cage present. Item cannot be deleted/destroyed, and other blocks can be placed in that spot.
Do not know how to duplicate; spawner appeared after version 11 update.
This bug was reported previously as MCPE-8680, to which this ticket has been linked.
To removed the spawner entity, place an empty monster spawner in it's place. Destroying the new cage will properly remove the entity.