Dear PerlMonks,
Following quote from Mark Minasi at link:
WindowsITpro Article 96375
explains this behaviour.
"Or what about the small-but-essential fact that adding an external manifest to a legacy program in hopes of solving a User Account Control compatibility problem works sometimes but not always, thanks to a glitch in the disk-caching algorithm?"
I guess we'll just have to wait praying that the next Vista Service Pack solves this issue.
Regards.
DDN123456