Same issue here with Surface Pro 2 and Wedge Touch Mouse (or razr orochi). Issue does not occur with the same mice on other devices on my network (galaxy tab 2 and two different windows 8 desktops). Really frustrating that a premium product like the Surface Pro 2 does not work properly with basic peripherals with bluetooth mice! This needs to be fixed ASAP.
As I stated before, this is not a Microsoft issue. This is caused by interference between 2.4ghz WiFi and the 2.4ghz bluetooth signals when the WiFi saturates the wireless bandwidth during large transfers. It happens with other mice besides Microsoft's and on other current generation computers including the Macbook Air's. It is probably due to the WiFi and bluetooth being combined on a single chip by Broadcom.
Using 5 ghz WiFi will fix the issue. That is the only possible fix.