I checked it and the reason is in the settings of packers.
The installer you downloaded is packed by (Win)RAR. In the Home version (in the Professional version as well, unless you change it), Standard Shield doesn't scan archives - it's not very useful and can slow down your computer a lot. So, the file is not detected as infected when you download it.
When you start the installer, it extracts the bsdhooks.dll into the TEMP folder - and at that moment, the file is detected as infected (the extracted DLL, not the EXE installer).
I really don't understand that "win32 mode" error, however... you're not the first to mention it, but I cannot reproduce it anyhow. What is the exact message?