[R] change in I(x) ? in R 2.6.0

[Patrick Giraudoux]

Dear listers,

I am trying to use an old script which was working well in the previous 
R version. It looks like if it no longer works in R.6.0. I have a model 
of the form:

glm(nath2$Positif ~ n + yearday + x + y + I(x^2) + I(y^2) + yearday:x + 
yearday:y, family = poisson, data = nath2)

and want to get predicts from a data.frame whose column names are:

 > names(data1)
[1] "x" "y" "yearday" "n"

x and y are geographical coordinates, yearday is equal to 120 and n 
equal 100; they are all numerics:

 > sapply(data1,is.numeric)
x y yearday n
TRUE TRUE TRUE TRUE

when I use the function predict:

 > z1<-predict(mod1b,newdata=data1,type="response")
Error: variables ‘I(x^2)’, ‘I(y^2)’ were specified with different types 
from the fit

Any idea about what goes wrong ?

Patrick