Sanne started a discussion around the semantics of clear on the dev list, but I couldn't find any issue in JIRA. Could you create an issue? 

I don't think the problem with clear() is restricted to state transfer, though. Even in a regular, stable cluster, executing a put(k, v) operation at the same time as a clear() operation could result in the key being inserted on some of the owners but not all. And I'm not sure even a global lock would help with that...