Link on djm900 and 2 cdj 2000

I'm havin a little problem with my setup.

I have everything linked by a belkin router which has always worked fine on the link side of things.

The problem now is that the link functions of grid quantize and live LEDs on the cdjs only work if I have them in channel 1 and channel 2 of the 900 nexus.

The strange thing is the link from the USB drive plugged into either of the 2 cdjs works fine whichever channel they are plugged into and allows me to play from the single USB drive.

I'm sure when I had everything set up before I moved house I could use any channel and it all worked.

Is the full link functions suppose to only work on channel 1 and 2 or am I doing something wrong.

Thanks in advance.

Fearny.