sort.int(S3object) strips class but not the is.object flag

If x has an S3 class then sort.int(x) returns a value
without an S3 class but which has the is.object flag set,
which, I think, causes identical() give a false/misleading
report:

   >  x<- structure(1:3, class="unrecognizedClass")
   >  y<- sort.int(x)
   >  t<- 1:3
   >  identical(y, t) # expect TRUE

   [1] FALSE

   >  identical(as.vector(y), as.vector(t)) # expect TRUE

   [1] FALSE

   >  dput(y)

   1:3

   >  dput(t)

   1:3

   >  class(y)

   [1] "integer"

   >  class(t)

   [1] "integer"

   >  is.object(y)

   [1] TRUE

   >  is.object(t)

   [1] FALSE

The files made by
   save(t, file="t.Rdata", compress=FALSE)
   save(y, file="y.Rdata", compress=FALSE)
differ in 2 places, where the first is presumably
the name of the object:
   % cmp -l y.Rdata t.Rdata
   36 171 164
   39   1   0
(The problem persists after a save/load cycle.)

This is on R 2.12.2 on Linux.  Sorry, I don't have 2.13.0
yet installed.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com