Noticed this one on automated testing against a real Accumulo + HDFS instance. The test tries to write an empty "_tmp" rfile into a tablet directory and verify that Accumulo removes it.
On a system with separated users (e.g. hdfs, accumulo, and a test user) and DFS permission enabled, I can't come up with a good way to ensure this works as intended.
Going to switch it back to a MiniCluster for now.