Although I have not yet received any feedback from the BitRock
support, I have meanwhile done some further tests. Most important
result is that the installer finished flawlessly after I changed the
"TEMP" and "TMP" variables back to the default
"%USERPROFILE%\AppData\Local\Temp".
I am interested to hear how the installer is intended to handle links
under Windows, because a link might also be contained within a
non-default installation path.