"no visible binding for global variable" and with() vs. within()

R CMD check does not object to this code when checking a package:

foo1 <- function (bar) {
    with(bar, {
        x })
}

but produces a warning:

foo2: no visible binding for global variable 'x'

in response to this:

foo2 <- function (bar) {
    within(bar, {
        x })
}

Is this an R bug, or at least, an inadvertent inconsistency?  Here is
sessionInfo() from my machine, right after starting an interactive session:

"no visible binding for global variable" and with() vs. within()

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