I am CC'ing the accessibility list hoping that they might have an insight to what is happening. I have quoted the original mail in full below for their sake.
I'm not yet a Stretch user but the Orca developer has submitted a patch to fix this bug : take a look at <https://mail.gnome.org/archives/orca-list/2017-April/msg00184.html>.
Best regards. -- Alex ARNAUD Visual-Impairment Project Manager Hypra - "Humanizing technology"