[ODE] Strange stops on a u-joint?

[Megan Fox]

I'm setting a u-joint up with two fairly standard axis - (1, 0, 0) and
(0, 0, 1).  I then set both sets of lo/hi stops to -1.57 and 1.57.  My
expectation is that I'll end up with my limb moving freely in the +z
hemisphere, but never rotating about the limb's axis directly.

(the limb is a long box, more or less, and it starts pointing straight up)

... but what I get is a limb that only moves freely in one half of
that hemisphere.


Now I assume I'm just misunderstanding how to set the stops in this
case (or, more specifically, how stops on different axis interact). 
Can someone shed some light on what I'm doing wrong here?


Thanks,
-Megan Fox