Yeah.. i've suffered this. Is not really a router fault, but the logic of the GPI box.
When you touch down on the RCP the GPI box polls the router for the current source on the chosen destination and stores it, it then switches the destination to the RCP camera source for the duration of the GPI. When you release the GPI it switches the destination back to the originally stored source value..
That's all well and good until you tigger a second GPI during the first... at that point the second GPI polls the router and get the first GPI's source value and not the desired original source.
Currently with the Blackmagic GPI Box there's no solution to this - eventually I used a third party box which worked perfectly
http://bmrouter.co.uk/ but the link appears to be dead now.