Hi Vit K,
Thank you for your interest in our CMS and getting in touch with us.
The behavior you describe by design: it is normal to get an URL like www.mysite.com/mypages/onepage.aspx when Sitefinity redirects to the page. If you select a page with name OnePage from the site navigation, though, the URL will be www.mysite.com/MyPages/OnePage.aspx.
Currently, there is no way to apply case-SENSITIVE rewriting rules.
Honestly, we have not considered that this would be an issue for users. We'll definitely take this into account for future releases. Hope this doesn't cause too much inconvenience.
We have updated your Telerik account for drawing our attention to this.
the Telerik team