Because softwaretype recipe uses its own configparser directly to rewrite software type buildout before running buildout, it turns all options into lower case.
See https://lab.nexedi.com/nexedi/slapos/merge_requests/227#note_48387 for background, where I git hit by this problem trying to use an option name PATH.
According to python documention of the module, configparser turns all options to lowercase and expose optionxform method to make it case sensitive. This is what buildout use to do, but now buildout switched to its own implementation of configparser - with slightly different API, but the point is buildout options are case sensitive, so it's non intuitive to have case insensitive options in the instance buildout.
I added tests for this recipe at the same time, I could not find any.
/cc @rafael @vpelletier @alain.takoudjou @jm
[edit: some confusions case insensitive/sensitive]