formula restriction in multinom?

Good Day: When I used: 
multinom(formula = Y ~ X1 + X2 + X3 + X1:X2 + X1:X3 + X3:X2 + X1^2 + X2^2 +
X3^2, data = DATASET),
I get estimates and AIC for the model containing main effects and
interactions only (no squared terms)...and FYI, all predictors are
continuous. Is this "normal" behavior? If I run this in S-Plus I get
estimates and AIC for the model containing all terms(including the squared
terms).

   Thanks,
   Mark Berry




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