Model import fails

I have a Chern-Simons-Portal.fr file containing the following:

M$ClassesDescription = {
V[4] == {
ClassName -> xb,
SelfConjugate -> True,
Mass -> {Mxb, 1},
ParticleName -> "~xb"}
}

M$Parameters = {
cW == {
Value -> 0.001,
InteractionOrder -> {QED, 2},
Description -> "X boson coupling to W bosons"},

cmu == {
Value -> 1,
InteractionOrder -> {QED, 2},
Description -> "X boson coupling to muons"}
}

I generate the model using the following code in Mathematica:

LoadModel["SM.fr", "Chern-Simons-Portal.fr"]
LoadRestriction["Massless.rst", "DiagonalCKM.rst"]
LCS := cW Eps[\[Mu], \[Nu], \[Alpha], \[Beta]] W[\[Mu]] xb[\[Nu]] del[
    HC[W[\[Alpha]]], \[Beta]] +
  cW Eps[\[Mu], \[Nu], \[Alpha], \[Beta]] HC[W[\[Mu]]] xb[\[Nu]] del[
    W[\[Alpha]], \[Beta]] + xb[\[Nu]] mubar.Ga[\[Nu]].Ga[5].mu +
  Mxb^2/2 xb[\[Nu]] xb[\[Nu]] -
  1/4 (del[xb[\[Mu]], \[Nu]] -
     del[xb[\[Nu]], \[Mu]]) (del[xb[\[Mu]], \[Nu]] -
     del[xb[\[Nu]], \[Mu]])
WriteUFO[LCS];

I do not have any warnings or errors during running the code. However, after opening a file parameters.py I see that the width of xb particle is defined twice:

Wxb = Parameter(name = 'Wxb',
                nature = 'external',
                type = 'real',
                value = 1,
                texname = '\\text{Wxb}',
                lhablock = 'DECAY',
                lhacode = [ 9000006 ])

Wxb = Parameter(name = 'Wxb',
                nature = 'external',
                type = 'real',
                value = 1,
                texname = '\\text{Wxb}',
                lhablock = 'DECAY',
                lhacode = [ 9000001 ])

When importing the model in MadGraph is have the following error:

Error detected in "import model ChernSimons_UFO"
write debug file MG5_debug
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
InvalidModel : name Wxb define multiple time. Please correct the UFO model!

I tried simply to remove the extra lines for the decay width, but the error remained. Where can be a reason?