Over-adjusted steering box locking up?

[1983/300CD]

I've read that adjusting the screw on the steering box can cause the steering box to lock up when the wheel is turned too far to the right or left.
My last alignment, I was given around 4 degrees caster. I didn't like the way it drove, but it was okay. The wheel turned back and forth. After reestablished the 8 degrees caster, it seems to stick when backing up turned all the way right.
When I pull backward with the wheel turned all the way to the right, then stop and attempt to move forward and turn to the left, the wheels stay locked to the right. If I move forward and back, it will allow me to turn the wheel again, and everything is fine.
I am wondering if this is typical of the over-adjustment of the steering box, or something else? Any ideas?