Moving the position down in 0.25 increments stops working when the Z position drops below zero

[electric-monk]

Attempting to drop the manipulator until the suction cup's limit switch hits an object, I was using the Python API like so:

while not arm.get_limit_switch():
        pos = pos - 0.25
        arm.set_position(x, y, pos, wait=True)

In older firmware this worked fine, but in the latest, after the Z position passes 0, the function will start blocking and never returning, or intermittently working, blocking the code from finding the object.