userstat / I_S.{client,user}_statistics missing most of data

Userstat feature, or tables INFORMATION_SCHEMA.CLIENT_STATISTICS and INFORMATION_SCHEMA.USER_STATISTICS are missing most of the data.

Server version:

Percona-XtraDB-Cluster-server-56-5.6.42-28.30.1.el6.x86_64

The configuration "userstat" is enabled:

# grep userstat /etc/my.cnf
userstat=1

But still the tables show almost nothing (note that I have redacted the IP address, the field "CLIENT" does show a correct IP address but ~all other fields are zero):

mysql> select * from client_statistics;
--------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| CLIENT | TOTAL_CONNECTIONS | CONCURRENT_CONNECTIONS | CONNECTED_TIME | BUSY_TIME | CPU_TIME | BYTES_RECEIVED | BYTES_SENT | BINLOG_BYTES_WRITTEN | ROWS_FETCHED | ROWS_UPDATED | TABLE_ROWS_READ | SELECT_COMMANDS | UPDATE_COMMANDS | OTHER_COMMANDS | COMMIT_TRANSACTIONS | ROLLBACK_TRANSACTIONS | DENIED_CONNECTIONS | LOST_CONNECTIONS | ACCESS_DENIED | EMPTY_QUERIES | TOTAL_SSL_CONNECTIONS |
--------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 00.00.0.0 | 6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| | 1 | 1 | 29940137 | 484 | 548 | 0 | 0 | 0 | 0 | 29149934 | 28300922 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 00.00.0.1 | 21328 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 00.00.0.2 | 1595541 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 000.000.000.1 | 26186 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 000.000.000.2 | 167 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 00.00.0.3 | 51582 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |

Is it a bug? If it is a limitation in PXC, would be nice to have it documented somewhere.