Logstash keystore, keys entered in UPPERCASE becomes lowercase

[Mattias_Arbin]

I have this strange issue with the logstash keystore.
I started adding one password in my keystore named ES_PWD
I am pretty sure I got my logstash config working by accessing the key as ${ES_PWD}

Now, after adding a few more keys, my keystore suddenly lists all keys in lowercase.
When I add a new key in uppercase letters, it seems to be stored in lowercase. See example below. Is this the expected behaviour?

# /usr/share/logstash/bin/logstash-keystore --path.settings /etc/logstash add TESTING

Enter value for TESTING:
Added 'testing' to the Logstash keystore.

# /usr/share/logstash/bin/logstash-keystore --path.settings /etc/logstash list

test
testing

Logstash version is 6.4.0
Red Hat Enterprise Linux Server release 7.4 (Maipo)

[Mattias_Arbin]

OK, after some experimentation I realize that the keys are case insensitive, e.g.
both {TESTING} and {testing} are accepted.
I had another issue that added to the confusion.

So, no big issue, except maybe that it could be clearified in the documentation that the keys are case insensitive.