wall/gran/hertz/history frictionflag

Hello.
What is mean of the frictionflag in wall/gran style?
I thought if the frictionflag is zero then the wall without friction. But the test showed that it is not.
In test script a sphere moves along yplane with given initial velocity. If yplane is frictionless then sphere's velocity should not be changed. But it is changing, see attached figs. And in different ways depending on the value of the flag.

And if I need frictional and frictionless walls should I to define 2 atomtype?
Thanks.

Test script:

#Particle packing by insertion and successive growing of particles

atom_style granular
atom_modify map array
boundary p m p
newton off
#echo both

communicate single vel yes

units si

#Simulation domain
region reg block -0.1 0.1 0. 0.1 -0.1 0.1 units box
create_box 1 reg

neighbor 0.002 bin
neigh_modify delay 0

#Material properties required for new pair styles
fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.3
fix m4 all property/global coefficientFriction peratomtypepair 1 0.5

#New pair style
pair_style gran/hertz/history 1 0 #Hertzian without cohesion
pair_coeff * *

timestep 0.00001

#Wall
fix ywalls all wall/gran/hertz/history 1 0 yplane 0. NULL 1

#Sphere
create_atoms 1 single 0 0.005 0 units box
set atom 1 diameter 0.01 density 2500 vx 0.1

#Gravity
fix gravi all gravity 9.81 vector 0.0 -1.0 0.0

#region
group nve_group region reg

#apply nve integration to all particles that are inserted as single particles
fix integr nve_group nve/sphere

#output settings, include total thermal energy
compute 1 all erotate/sphere
thermo_style custom step atoms ke c_1 vol
thermo 1000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes

#insert the first particles
run 1
dump dmp all custom 100 post/dump.wallfric id type type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius
run 50000