It seems that I found a workaround for the problem (it is still a bug in my opinion):
here is my mounting-script that works well:
delay 2
tell application "Finder" to open home
tell application "Finder"
try
mount volume "afp://username:password@mynas/share1"
delay 1
mount volume "afp://username:password@mynas/share2"
end try
end tell
tell application "Finder" to close home
I have it in the login-items.
It basicly does the following: Open the finder with the home-view. Then mount the two shares. After that closes the finder window.
(Replace username:password with the credentials needed to mount the share, "mynas" with the name or adress of the server and "share1", "share2" with the acutal name of the share.)
The 2 seconds delay at the beginning is not really needed I suppose but since the script works I'll leave it there.
In order to see the shares in the favorites section of the finders sidebar you have to drag them there once by hand. Afterwards they will show up there everytime the particular share is mounted.
The trick is to open the finder window before the shares are mounted. When the script does this they will appear in the sidebar. I think there is the problem. When the script mounts the share without displaying the finder window, they will not show up in the sidebar. It is a bug introduced with ML.