Fix PR#5892

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13250 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
add test case for PR#5892

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13251 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02