column names in matrix vs. data frame in R 1.8

White.Denis at epamail.epa.gov writes:

Is the difference in behavior below, introduced in 1.8, inconsistent

at least, undesirable?  I couldn't find this in the NEWS.

On the one hand,

a <- matrix (1:4, nrow=2)
a <- data.frame (a)
names (a) <- c("break","next")
names (a)

[1] "break" "next"

On the other,

a <- matrix (1:4, nrow=2)
dimnames(a) <- list (1:2, c("break","next"))
a <- data.frame (a)
names(a)

[1] "break." "next."

Works fine if you don't use keywords as column names

a <- matrix (1:4, nrow=2)
dimnames(a) <- list (1:2, c("foo","bar"))
b <- data.frame(a)
names(b)

[1] "foo" "bar"

The difference in the result for your example has to do with an extra
step in the second case to obtain a legitimate name that can be used
with the $ operator.  R generates a syntax error for

a$break

but not for

a$break.