moveit getJacobian

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Hi! I had a problem with moveit's computeVariableVelocity, which I tracked down to a weird Jacobian matrix in my model. The robot has X, Y and Z prismatic joints, then a Z revolute. But with the joint-states all zeroed out, I'm getting a jacobian

  1.304  0.31889  0.41454        0
  -0.03  0.97173 -0.06256    0.575
0.19219  0.23349  2.48029        0
      0        0        0        0
      0        0        0        0
      0        0        0        1

which looks very wrong in a bunch of ways (not least, 1m of Z joint movement turns into 2.4m of worldspace Z!). Only the final revolute joint looks right.

Stepping into getJacobian, things seem to go wrong around line 1161:

joint_transform = reference_transform * getGlobalLinkTransform(link);
joint_axis = joint_transform * static_cast<const robot_model::PrismaticJointModel*>(pjm)->getAxis();

When I hit this line, getGlobalLinkTransform returns a valid matrix that includes translation. There's nothing in reference transform to cancel this out, so prismatic axis gets rotated and translated, and joint_axis ends up totally wonky.

Is there something wrong with my RobotModel here? Am I misunderstandingt the Jacobian?