Yes because M5 is orbiting the barycenter, but as it is so close it barely moves, but it has to move somehow as it is still orbiting something else. As Kerrec said the orbital path is so small it's within the diameter of the star.
I think you'll find it's purely because M6 doesn't orbit M5. No matter how small the distinction may be, M5 is orbiting something other than the main star.
Right i see, i need these explanations because i don't understand half of whats being posted [blah] sorry for the snappy reply earlier i feel quite foolish now