We are not aware of such a bug and could not reproduce such an issue. I created a new community project of Sitefinity 3.5 and there were no problems in saving details of users (neither on the My Profile page, nor on Users).
Could you tell us more about your project. For example, send us which version exactly is the one you are using. You could get that from the page source of any of the public pages of the project, and find and copy the following meta tag info:
|<meta name="Generator" content="Sitefinity 3.5.1747.3" />
The highlighted numbers are taken from my project with which I tested.
Also, tell us if you are with administrative rights. Also, are you using active directory?
Anything you could tell may help reproduce the problem.
the Telerik team