I noiced that too. And it's not related to channels, because I was in the Academy and I couldn't target a party member that was in Novograd. If you're not in the same instance (same raid, same zone, same channel), you can't target them. Which sucks.
Actually.. the menu does work. And you can inspect players, but you won't be able to see his character and inspect addons (NISV,InspectEquipRatin) won't work. But you can see his gear.
just had it in a BG too, player was "far away" all the time, could not inspect or even click, but player participated
all other partymembers were normal