Joint Break Force Distance

I'm getting unexpected joint breaking behavior (or lack thereof) when using multiple kinematic rigidbodies. I've set up a simple test with three game objects: a. kinematic rigidbody b. rigidbody with a spring joint connected to "a" and break force of Infinity, as well as a fixed joint connected to "c" with break force of 1.0 c. kinematic rigidbody

As object "a" is move continually away from "b" and "c", I would expect the force to increase and eventually break the joint between "b" and "c". This does not happen. It does, however break if I move "a" erratically, just not when it's moved in a steady motion.

Any Ideas?

Oddly, when I change the fixed joint connected body to be "none", the joint does break when pulled too far. It also breaks, though at a different distance (again... odd), when I set "c" to be non-kinematic but have all movement constraints checked.