Keep the same state for the SYSREFREQ pin when switching from request mode to windowing mode and back to request mode. For example, if the SYSREFREQ pin is high (or low) when windowing mode starts, make sure the pin state is high (or low) again after windowing mode ends before programing CLKPOS_CAPTURE_EN.
The SYSREFREQ pin must be set low when switching from or to SYNC mode.