App duplication in iTunes library shared across two accounts on same iMac

Question

I'm sharing media across two user accounts on a family iMac running Yosemite. The shared content is distributed across folders (Audiobooks, Music, Mobile Applications, etc.) inside Users/Shared/iTunes Music. Both accounts have read and write permissions, and family and home sharing are both turned on and linked to one primary Apple ID. In both accounts iTunes preferences point to the same shared folder. The problem: Updates to mobile applications in one account do not carry over to the other. After updating mobile apps for account A, when I switch to account B, I get the same list of apps awaiting updates. If I update for each account, I find duplicates for each updated app in the shared Mobile Applications folder.
I can avoid the duplication by control-clicking, in the Updates window of iTunes in account B, an app that has already been updated in account A. That will open a dialogue window saying the original file can't be found and asking if I'd like to locate it. When I do, the update disappears from the list in the Updates window. However this is a cumbersome process that I'd think iTunes would perform automatically if it were functioning properly. Has anyone encountered this issue and found a better solution?

Answer 1

For iPhoto 09 (version 8.0.2) and later:
What you mean by 'share'.
If you want the other user to be able to see the pics, but not add to, change or alter your library, then enable Sharing in your iPhoto (Preferences -> Sharing), leave iPhoto running and use Fast User Switching to open the other account. In that account, enable 'Look For Shared Libraries'. Your Library will appear in the other source pane.
Any user can drag a pic from the Shared Library to their own in the iPhoto Window.
Remember iPhoto must be running in both accounts for this to work.
If you want the other user to have the same access to the library as you: to be able to add, edit, organise, keyword etc.
Quit iPhoto in both accounts. Move the Library to the Users / Shared Folder
(You can also use an external HD set to ignore permissions, a Disk Image or even partition your Hard Disk.)
In each account in turn: Double click on the Library to open it. (You may be asked to repair the Library Permissions.) From that point on, this will be the default library location. Both accounts will have full access to the library, in fact, both accounts will 'own' it.
However, there is a catch with this system and it is a significant one. iPhoto is not a multi-user app., it does not have the code to negotiate two users simultaneously writing to the database, and trying will cause db corruption. So only one user at a time, and back up, back up back up.