USRP N210 Loop back connection

I am trying to use the USRP N210 device as a transceiver with LFTX and LFRX daughterboards. I want to use the loopback cable setup. What I have found is that the USRP TX and RX are communicating without even without the loopback cable or antennas attached in the transmitter and receiver ends. I used the built-in examples of

QPSK Transmitter with USRP® Hardware and QPSK Receiver with USRP® Hardware

provided in MATLAB in this link: https://www.mathworks.com/examples/communications/mw/usrpradio_product-sdruqpsktx-qpsk-transmitter-with-usrp-reg-hardware

How does the receiver still receives data from the transmitter even if the TX and the RX aren't really externally connected? Could you please clarify this for me?

Thank you!

[eleliuql]

Hi, I notice the same issue with USRP E312. Did you manage to solve this problem?