I ran into this too. I found it was doing machine auth by accident. This is a security device so "machine auth is on by default" shouldn't be a thing at all. The job of Clearpass should be to say NO unless the admin specified a rule that says YES.
We have a GPO and all that for our wifi.. however, I noticed it when I manually configured on a test laptop that doesn't have the gpo applied and it authenticated without putting in creds and it didn't have the "use windows creds" box checked.
It's fixed and works but I couldn't disagree with Aruba's approach more.