Flex 900 Common Daughter Board

I am using the Flex 900 Common Daughter Board for the usrp. I am using
both
boards as recievers. The connection RX2 on the board will not work when
connected and selected by the dual source usrp in GRC. However, if I
select
the TX/RX and reconnect my line to that port it will work. I am
wondering
why the RX2 setting is not being accepted and also if there is a way to
fix
this. I am using gnuradio-3.2.2.

Thanks,

Sean