The issue here is not so much the use of the immutable list.

The "issue" is that we really do not need to clear the bag (collection) as part of the merge handling for this particular case. Specifically - when we are merging an unmodified managed collection, there is no need to perform the clear first. Unless I miss some case. Gail Badner, you seemed to have some thoughts on case(s) where this would not hold true - could you list them here? Based on that, maybe this is (1) something even less generally applicable or (2) something we simply want to not do.

Either way, outside of this stipulation.. merging a non-`@Immutable` immutable collection is not really a valid use case. FWIW, in the example you gave Valentin Aitken, the merge is actually completely pointless. Everything between the persist and commit would have no ultimate effect here.