R help - Nov 2010 - formulas with non-syntactic names and an Error() term

## This is an example where ``-quoted non-syntactic names work in
## simple formulas, but not in formulas with an Error() term.
## Is this intentional or an oversight when ``-quoted names were added?

tmp <- data.frame(y=1:6,
                  `x^1`=factor(c(1,2,1,2,1,2)),
                  `x^2`=factor(c(1,1,2,2,3,3)),
                  check.names=FALSE)
tmp
aov(y ~ `x^1` + `x^2`, data=tmp) ## ok
aov(y ~ `x^1` + `x^2` + Error(1), data=tmp) ## error
## Error in `[.data.frame`(mf, xvars) : undefined columns selected

tmp2 <- data.frame(tmp)
tmp2
aov(y ~ x.1 + x.2 + Error(1), data=tmp2) ## this is ok

## this is Windows R-2.12.0
## Rich

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