.exp files not deleted with drop database

The .exp file create when a database is backed up with Xtrabackup do not get deleted when the the database is dropped. This causes the error:
ERROR 1010 (HY000): Error dropping database (can’t rmdir ‘./zfoo/’, errno: 17)

ls –l /data/mysql/zfoo
-rwxrwxr-x 1 mysql mysql 953 Mar 8 16:16 ztest.cfg
-rwxrwxr-x 1 mysql mysql 16384 Mar 8 16:16 ztest.exp
-rwxrwxr-x 1 mysql mysql 8948 Mar 8 16:15 ztest.frm
-rwxrwxr-x 1 mysql mysql 98304 Mar 8 16:01 ztest.ibd

mysql> drop database zfoo;
ERROR 1010 (HY000): Error dropping database (can’t rmdir ‘./zfoo/’, errno: 17)

ls –l /data/mysql/zfoo
-rwxrwxr-x 1 mysql mysql 16384 Mar 8 16:16 ztest.exp

Any ideas how to fix this?

Workaround would be to manually delete zfoo directory.