Doxygen 1.8.1.2 HTML Help generation

Hello Doxygen-Community!
I'm currently helping my company to migrate from the old doxygen 1.7.x to
the current version 1.8.1.2 .
We use doxygen to generate a Microsoft HTML Help file from our source files
for API documentation and additionaly we have some non code .doxy files
which describe a small tutorial + introduction page.
When using doxygen 1.7.x the HTML Help file is generated perfectly but
1.8.1.2 scrambles the navigation tree of the HTML Help file. The navigation
tree is generated correctly for the html pages auto generated from source
files (we use \group and \ingroup to describe dependencies in the source
files), only for the tutorial + introduction pages (split into multiple
.doxy files, concatinated by /page and /subpage commands) the html help
navigation tree contains dead links and the subpages are not placed
correctly. 
After some experimentation i discovered that Doxygen 1.8.1.2 generates the
HTML Help navigation tree directly from the Doxygen layout XML file's
<navindex> tag (1.7.x generated it from the \page-\subpage hirachy), but
even if i create a link manually by using a <tab type="user" ... /> and
putting a  <at> ref to the wanted page into the href attribute, the resulting
link in the HTML Help navigation tree is dead.
Since the linking of the HMTL pages is working i inspected the HTML Help
source files and discovered that the hhc file structure is not correct as
the wanted pages get referenced incorrectly by, e.g.
"!tutorialfile.html.html" instead of "tutorialfile.html" . 

I am not sure if this is a doxygen bug, because while migrating our
documentation system i discovered that doxygen 1.8.x is much more sensive to
command syntax than 1.7.x is, so i'm not sure if this is caused by any small
mistakes in the .doxy files (this are the same files that 1.7.x generates a