permission settings changed

[xp boy]

in the process of trying to install software on my comp
(xp pro), it was recommended that i change some of my
software permissions in regedit.

i gave users and power users 'full control' in addition to
their 'read' privleges. however, when i did this, i
noticed that the check marks in the 'special permissions'
boxes were removed.

it turns out that doing this wouldn't have help the
installation any, so i returned the settings back to their
original configuration. users and power users are back
to 'read' only, but the 'special permissions' check did
not return. why is that? does it matter? i havne't noticed
anything strange, but since this is the first time ive
ever changed a registry, id like to know whats going on.
thanks in advance,

j