i just picked up a juki DDL 8500-7 auto backstitch, and i noticed that the little arm by the thread tension does not move like other machines i have (and have seen)  usually it will move up and down while its sewing, or go up when the foot is raised, but on the 8500-7 it looks to be bolted into place.  i took the cap off of the end of the machin and there is nothing that i can see that is broken or missing.  it actually has a little shield in the way.  is this normal or is this some cheap way to get the machine sewing (it sews multiple layers of denim no problem)

even though it works fine, it kinda bothers me as i feel like there is something wrong with it.  the picture below is of the two other machines i have, and the new one in the middle.  also, if anyone can help me with what the little arm is actually called, it would be appreciated