The shop messed up. The axle shafts go to about 1mm away from where that shaft with the gears is. It looks like they welded the plate to far in. I've never used those plates I just connect the gears.
Edit, cant get pics to load but look at how close the axle shafts are to the shaft with the gears is.
http://www.240-sx.com/welding-your-differential/