Parallel 50 Ohm with Calibration

My customer put input pins with the following assignment on Stratix IV.

IO: Input

IO standard: SSTL-18 Class I

Termination: Parallel 50 Ohm with Calibration

(RUP and RDN are connected to resistors respectively)

The customer configured their FPGA and measured the input resistance at the pins.

But the customer said that parallel termination seems not working.

I reproduced this issue on SIV dev kit. 100ohm resistance was not monitored at all on these input pins.

Have you ever measure the resistance of Parallel 50 Ohm with Calibration on your board?

I have no idea why 100ohm resistance was not monitored