trailing comments prevent whitespace removal

I would expect make to remove trailing comments and then strip
surrounding white space from variable definitions as usual but it
seems that the comments prevent further stripping:

$ cat Makefile

# a classic var
FOO = foo

BAR = bar   # and another but commented differently

echo_some_vars:
        @echo "X$(FOO)X"
        @echo "X$(BAR)X"
---------------------------------------------------------------------------
$ make echo_some_vars
XfooX
Xbar   X