I'm sorry to break the silence.
John, I know you're tired of this - but the problem is that
App\gimp\lib\gimp\2.0\plug-ins\help-browser.exe hasn't
been replaced in 2.8.0 Rev 4 with the working one from
GIMP_Portable_Help_Fix_2.8.0.paf.exe
Just be aware that help-browser.exe must reside in the
App\gimp\lib\gimp\2.0\plug-ins folder.
In the above-mentioned fix it was mistakenly placed in
App\gimp\bin folder alongside with libgtkhtml-2-0.dll
The size of the working file is 54792 bytes.
The one with the size 46144 bytes doesn't work.