I asked Diatec about this and they said that the factory may have mixed some uncoated or coated (from another batch) Ctrl, Alt, and Windows keys on the keyboards since they need to remove the Vista key during the coating process. Yes it is odd, but it is not visible under normal lighting conditions so I don't see it as a big problem. Unfortunately all I have available for replacement is uncoated keys, so this wouldn't be any different.
I have asked Diatec to investigate the problem and I hope to offer future boards without the Vista bubble key at all, which would eliminate the need to remove these keys in the first place.