Using Qt Assistant to reference https

We have a successful Qt Assistant based help system running on 4.7.0 on Windows 7. We can reference locations on the company web site using links from html documents which have been wrapped into qch/qhc combinations using the usual tools.

However links to internal https:// based urls fail returning a blank new tab in assistant. But if we remove the 's' and use http://..... we are successfully re-directed to the https site. So we can make our system work if we edit our source links to remove the 's'.

Strikes me as odd. Anyone come across this and have a view on whether this is a bug or not?