Done exactly what you suggested (while you were typing the suggestion :-)

Have checked: HKLM\System\CurrentControlSet...
HKLM\System\ControlSet001 and 002
HKLM\Software\Microsoft\CurrentVersion\RunOnce
and RunOnceEx
HKLM\Software\WOW6432Node\......\RunOnce

Although install ended with message System must be restarted....
None of the locations had any files pending. NO FILES PENDING.
The \PendingFileRenameOperations node is not there.

So.... ????