Entering a new Namespace into a Niagara Parameter Collection appends the previous namespace to all parameters currently in the Collection
Once this issue occurs, any change to the NPC's Namespace is not reflected in the Parameters within the NPC, nor in other Niagara editors. The user has to manually rename the parameters within the NPC so that they will use the Namespace set in it.
Note that this automatic renaming does not appear to solve references to the parameter when it is used by other Niagara editors even though the parameter shares the same naming as it did prior to being renamed.
Additionally, it appears that I am unable to delete parameters from the NPC that have been renamed in this way. I have to manually rename the parameter before I am able to delete it.
Result: The parameter is renamed to NPC.TestNamespace.MyParameter
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-87607 in the post.