Wow, I can't believe VMware hasn't said this is a bug then since it worked in prior versions of vCSA. My old vCenter is version 5.1 running on Windows without this issue, so I thought it was related to the appliance. Guess they broke it when moving vCSA from 5.1 to 5.5. I wonder if the Windows version of vCenter 5.5 also has this issue.
No workarounds besides using a login without spaces. I actually prefer spaces, it's 2014, spaces should not be an issue.
Edit: Like mentioned above you can create a local SSO user WITH spaces and it will work. So I guess that is a workaround...