The installer installs both 32bit and 64bit instances.

Windows 64bit has two separate install paths for these -- %PROGRAMFILES% for the "native" binaries and "%PROGRAMFILES% (x86)" for the 32bit binaries as the system is 64 bit. (If the latter does not exist, the system is 32bit.)

So, the initial install location should always be taken from %PROGRAMFILES%.

However, I think the installer is likely built as a 32bit program -- so, because Windows isn't running in native mode, it gets told "%PROGRAMFILES%" is "%PROGRAMFILES% (x86)". That, of course, is then wrong on a 64bit system.

In addition, even if I manually tell the installer where I want it to install, the next time it runs, it doesn't bother to read the install location (that the uninstaller uses, so the installer set and should know how to read) -- it just defaults back to that incorrect location again.