Hinge rigid body constraint: question/problem

I defined a hinge between 2 objects. Isn’t it supposed to allow only rotations around the (empty’s) z-axis? But I clearly see a linear movement along the y-axis of the empty (in this case downwards) as well. How can that be?

You must enable limiting of movement.

Increasing physics steps should solve that but at exponential increase in CPU usage.

@adrian: where can I limit it?
@Jackii: I tried 1000 iterations, but didn’t seem to influence it.

On the constraint on the botom there must be checkboxes saying “limit”.

@adrian: For my constraint empty, on the physics tab, I only get Limits for the Z-angle, and I constrained that (-5 to 0). But it didn’t help.
But no limits for the z-axis anywhere?

I seem to get better results when choosing “convex hull” instead of “mesh” (although the test geometries have a very low vertex-count),
and when stying with low steps and iterations, like 10.