Python Client Executable priority incorrect for PYFLINK_CLIENT_EXECUTABLE environment variable

The documentation for configuring the python client executable states: 

The priority is as following:
1. the command line option "-pyclientexec";
2. the environment variable PYFLINK_CLIENT_EXECUTABLE;
3. the configuration 'python.client.executable' defined in flink-conf.yaml

I set python.client.executable to point to Python 3.6, and submitted a job that contained Python 3.8 syntax. Running the job normally results in a Syntax Error as expected, and the pyclientexec and pyClientExecutable CLI flags let me override this setting and point to Python 3.8. However, setting the PYFLINK_CLIENT_EXECUTABLE did not overwrite the python.client.executable setting.

export PYFLINK_CLIENT_EXECUTABLE=/usr/bin/python3.8
./bin/flink run --python examples/python/table/batch/python38_test.py

Still used Python 3.6 as the Python client interpreter.