This is common.  What happens is the combined network can support an MX, even though one isn't configured at the moment, and as such can have a firmware version set.   You can use this to do things like set the desired firmware for a new network before adding an MX to it. I've used it as well when swapping out an MX from a network for a new MX, and the old MX and new MX could not run the same firmware version due to the age difference. ... View more