particles fly out of boundary

Dear all,

          I am packing some particles in one cylinder using randomDensePack and append one wall upwards. Why did the particles fly out of the boundary?

          BTW, warning information exists after the randomDensePack:

No suitable packing in database found, running PERIODIC compression
/home/vigoss/myYade/install/lib/x86_64-linux-gnu/yade-Unknown/py/yade/pack.py:296: FutureWarning: The default behavior will change; specify returnSpherePack=True for the new behavior, and False to get rid of this warning (your code will break in the future, however). The returned SpherePack object can be added to the simulation using SpherePack.toSimulation()
  warnings.warn('The default behavior will change; specify returnSpherePack=True for the new behavior, and False to get rid of this warning (your code will break in the future, however). The returned SpherePack object can be added to the simulation using SpherePack.toSimulation()',category=FutureWarning)

from yade import pack

O.bodies.append(wall((0,0,0.01), axis=2, sense=-1, color=(0,0,1), mask=1))

O.bodies.append(geom.facetCylinder(center=(0,0,0), radius=0.005, height=0.02, orientation=Quaternion((0, 0, 1), 0), segmentsNumber=100, wallMask=6, angleRange=None, closeGap=False, radiusTopInner=-1, radiusBottomInner=-1))
pred=pack.inCylinder(centerBottom=(0,0,-0.01),centerTop=(0,0,0.01),radius=0.005)

O.materials.append(FrictMat(young=30e9,poisson=.3,frictionAngle=.5))

spheres=pack.randomDensePack(pred,radius=0.0008,color=None,rRelFuzz=0.00005, spheresInCell=400,memoDbg=False,memoizeDb=None)

O.bodies.append(spheres)