Have a look at the specs for the radios and do the link loss sums.
10 watts output power =10dB=40dBm
Rx sensitivity approx -110dBm
Difference is 150dBm
Co channel/adjacent channel rejection 60dB
So you're looking at achieving 90dB of isolation between the antennae
The figures are an educated guess but basically you're driving the receiver's front end into overload and causing the break through
