Problem with temperature compensated detector when input signal is OFDM

The attached file is a schematic from an Agilent AN. It is a temp compensated detector. I tested it with a CW in and it works perfectly in the rang -10°C 70°C, but when the input signal is a OFDM everything changed. The error in power measuring can be even 3dB or more. Any ideas?
thank you
molloy