OK, several things are much clearer now:
The ‘/log’ was basically my fault. My Zsh expanded
/log before invoking
cmd.exe; I should have noticed that.
More importantly, I got closer to the Blue Screen problem. Following your advice, I first erased the old IDE installation, but when I did a
rm -rf from my Cygwin Zsh on this directory, this command caused a Blue Screen immediately. Perhaps, the installer also erases the directory first, and stumbles over this problem. After reboot, I erased the directory from Windows Explorer, which worked without Bluescreen, but I found that some files (example: lib\mozilla\chrome\en-US\locale\branding\brand.dtd) needed me to enter my administrator’s password, in order to delete them. I wonder why this is necessary, since not every user will have local admin rights, and I think this is the original cause of the problem: While Windows explorer asks the user for the necessary credentials, some Windows function simply respond with a Bluescreen if an application does an
unlink of a file, instead of simply rejecting the request. If my theory is correct, this is of course a Windows bug, but still it makes me wonder why you are installing files which can not be removed with only user privileges.
Finally, when I installed the nightly build in a fresh directory, it worked well.