I have the same problem too with the loose case. Just got my RF 87U 45g uniform. I was really disappointed when I found out because it makes it feel sort of cheap, but knowing that it's a common issue kind of made me feel a bit better cause now I know I don't have a DOA.
Other than that, the keys type like a dream and feel great. I did email EK about this issue and here's what they had to say:
"The top of the 87U probably moves around more than most keyboards, as it is a screwless case design, but if you're not satisfied with it, we can replace it. However, we cannot not guarantee we can satisfy your subjectivity! Let me know if you'd like us to set up a replacement."
Pretty nice of them huh? I think I'm just gonna keep my current since, like they said, there is no guarantee and then I'd just be wasting my time and money if I got the same exact issue with a replacement. Also, I really just wanna keep my 87U nearby at all times since I'm pretty much in love with it now and can't possibly part ways with it for more than 2 minutes. By the way, my WPM increased by like 20 within an hour of using this keyboard compared to using MX blues before.