Thanks for contacting us and for reporting this issue.
I have investigated the case and indeed there is a memory leak when using the Visual Style Builder in Visual Studio. We are going to take a look at it and will try to provide a fix as soon as possible. FYI, we have been working on a new [much simpler] version of the Visual Style Builder, which will not exhibit such behavior. Thanks for bringing our attention to this.
I have updated your Telerik points for bringing our attention to this.
the Telerik team