Version Found: 2016.3
The 2016.3 High Speed SelectIO Wizard incorrectly allows you to choose Delay Mode = COUNT for RX synchronous designs.
Note: this Answer Record should not be viewed in isolation. For all other known issues and to see what version of Vivado / High Speed SelectIO Wizard these issues have been resolved in, please refer to (Xilinx Answer 64216)
This issue is resolved in the 2016.4 version of the High Speed SelectIO Wizard.
Delay Mode = COUNT is only recommended for Asynchronous RX designs. You should use Delay Mode = TIME for all synchronous designs.