[R] Bug in "is" ?

[ctu at bigred.unl.edu]

Hi R users
Is there anything wrong in "is" function? (R 2.7.2)
I believe that everyone will agree that "7" is an integer, right? but  
why R shows 7 is not an integer

> is.integer(7)
[1] FALSE
> is(7,"integer")
[1] FALSE
> is(as.integer(7), "integer")
[1] TRUE

Thank you very much in advance
Chunhao