For the 16-bit SPI-3 PHY Core, the TMOD signal is 2-bits wide in the design example testbench , while the signal on the core is only 1-bit wide. The upper bit is always undefined, and the lower bit takes in the value from the core.
To work around this issue, just look at the LSB of the TMOD signal in the design example. The MSB of the TMOD will not affect the functionality of the design. The testbench will be updated in the next release.