A customer created a directory `child` under `parent`. `child` was given the requisite ACLs to allow Impala to modify it, `parent` was not.
After this, they issued a "CREATE TABLE .. LOCATION `child` AS SELECT .." statement, which executed fine. And Impala was able to query and add data to this directory.
When they issued a "DROP TABLE", impala did drop the table in the metastore but was not able to delete the `child` directory as it did not have write privs for `parent`. I was unable to find logging to indicate this error - we looked in all Hive logs, and all Impala logs.
We tracked it down eventually by manually deleting the `child` directory, and then issued the CREATE, at which point we got an error back for the missing privs. It was also logged in the Catalog server logs.