Let's say i have very simple yaml config with envs:

default:
  my_section:
    my_param: "default settings content"
development:
  my_section:
    my_param: "development settings content"

And i want to override my_param with env variable at some point. What's proper env var name for such case? DYNACONF_MY_SECTION__MY_PARAM works if merge_enabled=False.
However, if merge_enabled=True, DYNACONF_MY_SECTION__MY_PARAM will set my_section.MY_PARAM, not my_section.my_param.
Easy reproducer:

import os
import dynaconf


os.environ["DYNACONF_MY_SECTION__MY_PARAM"] = "env var content"

settings = dynaconf.LazySettings(
	environments=True,
	env="development",
	settings_files=["settings.yaml"],
	merge_enabled=True,
)

print(settings.my_section.my_param)
print(settings.my_section.MY_PARAM)

Running the code returns the following output:

development settings content
env var content

setting merge_enabled=False and re-running the code returns expected output:

env var content
env var content

Documentation is kinda confusing about this behavior, so i'm not 100% sure it's a bug:
On the one hand, https://www.dynaconf.com/envvars/ examples are showing uppercase env vars are correctly recognized:

export DYNACONF_PERSON__IS_ADMIN=true
assert settings.person.is_admin is True

And it works like that with merge_enabled=False
On the other - there's the following line:

Also variable access is case insensitive for the first level key

And there's https://www.dynaconf.com/configuration/#lowercase_read , so it looks like only the first level keys are designed to be case insensitive.

I'm using dynaconf 3.1.7, OS is macOS 12.2.1 if that matters.