strange increase in the reference number

Hi,

I just found a strange increase in the reference number and I'm wondering
if there is any reason for it, here is the code.

a=c(1,2,3)
.Internal(inspect(a))

@0x000000001bf0b9b0 14 REALSXP g0c3 [NAM(1)] (len=3, tl=0) 1,2,3

is.vector(a)

[1] TRUE

.Internal(inspect(a))

@0x000000001bf0b9b0 14 REALSXP g0c3 [NAM(7)] (len=3, tl=0) 1,2,3

The variable *a* initially has one reference number, after calling
*is.vector* function, the reference number goes to 7, which I believe is
the highest number that is allowed in R.  I also tried the other R
functions, *is.atomic, is.integer* and *is.numeric* do not increase the
reference number, but *typeof *will do. Is it intentional?

Best,
Jiefei