Actually this is working as intended starting with NX 10.0.
There is a rather brief description of what and why this was done in the 'What's New Guide' in the section titled...
System Administration -> Internalization and Localization -> Using local language in NX applications
Granted, it doesn't say a lot except that you can now use the same character sets for File, Attribute and Expression names as well as in some other places in NX as are supported for the various languages that NX can be run using. This includes not only most all of the special Roman characters like the ones you mentioned, but also character sets like Chinese, Japanese, Korean, etc.
The only characters which are not allowed are those which both LINUX and Windows explicitly disallow for item naming
John R. Baker, P.E. (ret) EX-Product 'Evangelist' Irvine, CA