Ups I was wrong (and I guess you'll see that with test failures :-) )
With fine grained locking for atomic keys in place, we do the following:
- on the node that owns the atomic map (cdl.localNodeIsOwner(command.getKey()) we acquire locks for each individual key placed in the map (command.getCompositeKeys()) 
Why not acquire lock on the AtomicMap key itself? well in order to allow multiple tx updating the same atomicMap, as long as they operate on a different key set.
This makes me think there is a bug on the lock acquisition side as well, as there we filter out keys that don't map to the local node - and we shouldn't do that for CompositeKeys. @pruivo  can you please add this comment + a unit test to verify that locking works as expected for AtomicMaps (+ most likely a bug as I don't think it does work as expected :-)