gdebi doesn't grant administrative rights

This bug is _exactly_ the reported Bug #76300 " with the only one difference: It occurred on Ubuntu Feisty 7.04 DVD-iso:
To be sure this is a bug indeed before reporting, i have formatted my HDD 2x times and have set up at both times a virgin Feisty (=without any custom changes), then tried to install the first deb package on this system => problem came up:

Binary package hint: gdebi

Steps to reproduce the bug:

1) Open Synaptic and type root password (purpose: to force gdebi to remember the password)
2) Close Synaptic

3) Open Terminal and type sudo -s, then type root password (purpose: to force gdebi to remember the password)
4) Close Terminal

# Up to here i "should" have 15 minutes times to use gdebi before i have to re-type my password again. It was on Edgy so.

4) Download a *.deb file;

5) Double-clicking the file opens it with gdebi;

6) Hit "Install Package";

7) gdebi says that administrative rights should be granted;

Expected result: gdebi asks for administrator password and installs the package thereafter.

That is clear to me, gdebi does not remember the administrator password .
By entering the password to install this deb package, gdebi will ask the password again by installing the next deb packages.

It happens to all deb packages, what ever chmod they have.
I am the admin (the standard account was created while install process Feisty with all privileges)

The problem does not occurre on a LIVE-DVD system, only on the installed one.
Synaptic + Terminal can remember password during the 15-minutes, except gdebi.

System: Vaio Notebook
OS: Installed Feisty 7.04 DVD ISO version
Version gdebi 0.2.4ubuntu1 (the original one on the DVD)