2 radios, same network, different PC's

I just noticed this behavior and can't figure it out, may be something I have done.

I have a 6600 and an 8600 on my network with a PC for each. The 8600 is using transverter 1 on 630 meters and has TX1 as the push to talk. The 6600 is on transverter 1 on 144 MHz also using its TX1as ptt1. The 8600 is using CAT COM 4, the 6600 is using CAT COM 7 (they were the same but I changed them to see ). When I key the 8600 from Smart SDR, both radios key up the transverters. However, when keying the 6600 from SDR on the other PC, it is the only radio activated. Of course, turning TX off on the 6600 fixes the problem but changing the com port didn't.
I hope I explained this well enough.
Thanks for any ideas.

Tom

N9RU