It seems you are currently running Test Studio version 2011.1.712. This can be verified on the Help tab in the lower left corner.
We have support for Safari 5.1 since version 2011.1.729. Please upgrade to our latest internal build 2011.1.809. This is available for download on the "Your Account" page on www.telerik.com
under the Internal Builds Downloads section. Here
is a direct link.
Let me know if you need further assiatance!
the Telerik team