psql leaks memory on query cancellation

Here are the steps to reproduce a leak:

1. connect to 10.3 server, perform the query similar to:

select 'message' || generate_series(1,1000000000);

2. monitoring psql memory usage in htop or similar tool, press ctrl+c at some point where you can clearly distinguish a psql with a big allocated buffer from psql without it.

3. see the query cancelled, but psql memory usage stays the same.

This is especially painful when query you're debugging has a runaway join condition, and you understand it only after it doesn't return in seconds as you've expected.

Is it expected behavior (so I can have a look at something server returned somehow and it's kept there for me), or a plain leak?