Commit Xavier's fix for #6032.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13750 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Non-regression test for #6032.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13751 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02