Its possible to create user groups through the Java API that contain upper-case characters in the name. Confluence itself prevents such groups from being created though its UI.
Why does the UI not allow this? What problems are caused by creating such a group?
In a wonderful world - the api wouldn’t do it. It causes problems in the ui world since you could end up (and will end up) with:
Each one can have their own list of users so each one is valid.
So why is this bad? Well if you’re saving the group name in your settings somewhere - and then the admin changes the casing of the group - that should cause any problem right (because Dwester is the same as dwester)? Queue the support tickets…
So why does the api allow it? External evil directories that allows it (but they have more metadata about the groups) and we’re left with cleaning up after them.
Not that I have any opinions about it. 
Ah yes that makes sense, thanks Dan. An old version of one of our apps allowed upper-case characters to be used during creation of a group. Was just trying to gauge what impact that would have had going forwards. Luckily the UI of both app and confluence were already doing case insensitive checks before allowing variants of same name to be created.