[CMake] cmake 2.6-RC-8: Problem with WxWidgets 2.8 on OSX 10.3

[Honest Guvnor]

OSX 10.3.9 (gcc 3.3)
cmake 2.6-RC-8
wxwidgets 2.8.3

In moving from cmake 2.4 to 2.6-RC-8 the WxWidgets support is failing.
When compiling wxwidget code I am seeing commands from cmake like:

/usr/bin/c++   -D_FILE_OFFSET_BITS=64 -D_LARGE_FILES -D__WXMAC__
-fmessage-length=0 -D__WXMAC__ -I/Users/andy/work/taf/trunk/include
-I/Users/andy/work/taf/trunk/include_config -isystem
/usr/local/lib/wx/include/mac-ansi-release-static-2.8 -isystem
/usr/local/include/wx-2.8   -o CMakeFiles/gg2dgui.dir/gui.cpp.o -c
/Users/andy/work/taf/trunk/gg2dgui/rubbish.cpp
In file included from /usr/local/include/wx-2.8/wx/wx.h:15,
                 from /Users/andy/work/taf/trunk/gg2dgui/rubbish.cpp:16:
/usr/local/include/wx-2.8/wx/defs.h:609: error: template with C linkage
In file included from /usr/local/include/wx-2.8/wx/memory.h:16,
                 from /usr/local/include/wx-2.8/wx/object.h:20,
                 from /usr/local/include/wx-2.8/wx/wx.h:16,
                 from /Users/andy/work/taf/trunk/gg2dgui/rubbish.cpp:16:
/usr/local/include/wx-2.8/wx/string.h:994: error: declaration of C
function `wxString operator+(const wxString&, char)' conflicts with
/usr/local/include/wx-2.8/wx/string.h:992: error: previous declaration
`wxString operator+(const wxString&, const wxString&)' here
/usr/local/include/wx-2.8/wx/string.h:996: error: declaration of C
function `wxString operator+(char, const wxString&)' conflicts with
/usr/local/include/wx-2.8/wx/string.h:994: error: previous declaration
`wxString operator+(const wxString&, char)' here
...

If I replace the -isystem /usr/... with the conventional -I/usr/...
then it includes the wxwidget headers without complaint.

The project has a wxwidgets C++ main with both Fortran and C
libraries. I can post more if the problem is not clear.