File sharing problems and horror story (nearly)

Question

I use Leopard on a MacBook Pro, a MacBook and a iMac G4 800 MHz (unsupported model).
I have on the iMac and the MacBook Pro many users (the same ont he two machines) and I always use Fast User Switching.
I have had very few problems with Leopard until now; I like it even if there are some glitches or some new features which are not my cup of tea (hierarchical menus missing from the dock, stacks useless when there are many items, FireWall impossibilities (?) to open specific ports, Back to my Mac working on a Lan but not from outside until now, problems with a few apps (Parallels networking erratic), ...
Now about File Sharing.
Let say my main account is user1 (Administrator), and I have another user2 also administrator, plus user3, user4 standard users.
On the iMac I activate File Sharing.
On the MacBookPro, as user1, if I connect to the iMac Server (using afp://IPaddress_of_theiMac/) I do NOT get the dialog
"Enter your user name and password to access file server YYY
Connect to server as Guest or as Registered User"
but I directly get the dialog
"Select the volumes you want to mount on YYY"
From this, if I select user1 it mounts with full read/write permissions which is normal. It appears that I am connected with my Apple account user1&mac.com (same as mentionned in the Account panel of System Preferences).
On the other hand, if I try to connect to the user2 account, I only get limited access although in the File Sharing Preferences, user1/iMac is mentionned with full Read/Write preferences for the Home Folder of user2.
What is very surprising is that if I log on the MacBook Pro as user2, or user 3 or user4, then connect to the iMac, I first get the dialog to enter a user name and a password. This gives me access with the correct full permissions on user1/iMac or user2/iMac using the corresponding user name/password pair; this is the usual behaviour which is missing when trying to connect from user1/MacBook Pro.
Now for the Horror Story!
Trying to understand what was going on with the permissions of the user2/iMac account, I logged in to the iMac as user1, went to the Users folder and from there had a look on the informations about user2 home folder. In the lower part of the pannel, Sharing & Permissions says "You have no access" (which is normal) and this is followed by a table where users and permissions are listed. It seems user1 has Read and Write access in contradiction with the preceding phrase...
Anyway, I tried to modify these authorizations for user2 by clicking on the lock of the Information pannel and entering name and password of the administrator. Didn't go farther than that. By mistake, I hit Command-Delete and user2 was GONE from the list AND NOT ONLY from the list in the Information window! Using Fast User Switching and going to user2, nothing left on the Desktop and NO Home anymore.
In the System Preferences/Accounts panel, user2 was still mentionned.
In the Users folder, no user2 folder anymore.
Using once again Fast User Switching, I logged as user2 and got by magic an all new Home. Nothing left in Documents, Library or other user1 folders. Standard settings for icons, dock, etc.
My first move has been to use a very recent backup to restore everything (Thank you Mike Bombich from Copy Cloner!).
Once everything was back to normal, I had a look at the Trash from user1 and guess what, the Home folder of user2 was there, complete.
So now I am left with two questions
why is it I do not have the same dialogs when connecting from all the accounts although as far as I can see, configurations are the same?
why is it possible, from an Information pannel to delete the account of another user?
Thank you all for comments!

Answer 1

For the file sharing problems, answer is found in
http://docs.info.apple.com/article.html?artnum=306723