memory leak in Galera-4

Galera wsrep layer leaks memory on nodes receiving writesets.
For some reason any issued DDL on master makes such nodes release some of the leaked memory (but doesn't stop the leak).

This is affecting a customer of ours.
It is clearly seen that the leak is in wsrep layer because if node gets evicted (wsrep layer is shut down but mysqld stays up) all memory is released instantly.

Besides, the nodes where the leak appears are receiving NO queries at all.

Leak only affects nodes receiving writesets via wsrep layer - master is NOT affected.

How to reproduce: 3 Centos7 nodes, 1G memory on each, use supplied sysbench script and leave it running for few hours.

sysbench --db-driver=mysql --mysql-host=localhost --mysql-user=root code.lua --tables=16 prepare

sysbench --db-driver=mysql --mysql-host=localhost --mysql-user=root code.lua  --tables=16 --threads=64 --time=0 run