In `AtomicMapAPITest#testAtomicMapAfterFineGrainedAtomicMap` we test that one entry cannot be mapped to both fine- and coarse-grained atomic map. However, the test relies on local node being owner, because the check is based on type of the proxy - but the proxy is not persisted in cache.
So in practice you can access the fine-grained map as coarse-grained and vice versa.