BUG #15250: ERROR: could not find pathkey item to sort

The following bug has been logged on the website:

Bug reference:      15250
Logged by:          Sara Pranke
Email address:      sara.pranke@gmail.com
PostgreSQL version: 9.4.17
Operating system:   Debian 8.0
Description:

I have complex queries in large tables that use memory for sorting items, we
upgrate PostgreSQL from 9.1 to 9.4 and in this version we get this error:
'could not find pathkey item to sort'

I increased the work_mem to 1GB and this improved the performance and avoid
the error, but with the pass of the day is like the memory is not liberate
and crash to another queries with sorting itens, causing the error.

I searching about this error and the last report is in version 9.3.5.

In some point (something about of end at the day) the memory is liberate and
is possible execute the same queries that was not possible before.

We have replication and the config is like this;

shared_buffers = 4084037kB
work_mem = 1000MB
checkpoint_segments = 96
checkpoint_completion_target = 0.9
wal_buffers = 16MB
listen_addresses = '*'
wal_level = 'hot_standby'
archive_mode = on
archive_command = 'cd .'
max_wal_senders = 4
hot_standby = on
wal_keep_segments = 32
effective_cache_size = 10GB
maintenance_work_mem = 1GB
default_statistics_target = 100
random_page_cost = 1.1
effective_io_concurrency = 200
max_connections = 500
superuser_reserved_connections = 5
dynamic_shared_memory_type = posix