Calimero effect in plot3d

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just out of curiosity, what is the reason for this Calimero effect ? ?

from sage.plot.plot3d.plot3d import axes
var('x,y,z,r,alpha,beta,gamma',domain='real')
#rNum=1;alphaNum=0;betaNum=pi/4;gammaNum=pi/4
#rNum=1;alphaNum=pi/7;betaNum=pi/7;gammaNum=pi/7
rNum=1.0;alphaNum=pi/12;betaNum=pi/8;gammaNum=pi/6

numL=[r==rNum,alpha==alphaNum,beta==betaNum,gamma==gammaNum]

eqS=r^2==x^2+y^2+z^2

X=solve(eqS,x)[1].rhs()
Y=solve(eqS,y)[1].rhs()
Z=solve(eqS,z)[1].rhs()
Znum=Z.subs(numL)

S = matrix(SR,[X,Y,Z]).transpose()
Snum=S.subs(numL)
#show('S : ',S,'\t S num : ',Snum)
Plt=plot3d(Znum, (x,0,rNum), (y,0,rNum) , frame=False, color="blue",opacity=0.1)
# plot the three axis
Plt+=arrow((0,0,0), (rNum,0,0), color='black')
Plt+=text3d("X",vector([rNum,0,0])*1.1, color='black')

Plt+=arrow((0,0,0), (0,rNum,0), color='brown')
Plt+=text3d("Y",vector([0,rNum,0])*1.1, color='brown')

Plt+=arrow((0,0,0), (0,0,rNum), color='red')
Plt+=text3d("Z",vector([0,0,rNum])*1.1, color='red')
margin=0.1

show(Plt,xmax=rNum+margin,ymax=rNum+margin,zmax=rNum+margin)