Right. I forgot to switch the staging on the 1.25m decoupler, but it's the same anyway if it is switched. And you're right, I tested it by rebuilding it beginning with the rover body as the root part and it took the mass into account.
I just wanted to run this by you in case it isn't an intended feature. The readout in the VAB doesn't take into account the weight of objects attached by decouplers or stack separators. http://imgur.com/a/k3Sml#0