The library group feature "Limit item editing by group" prevents you from editing items from other libraries, but it fails to prevent the following two scenarios: 1. You can add a new item for other libraries outside your library group On Bug 20256 Comment 42 Jonathan mentions this as an issue, but it doesn't look like it was discussed further after that. 2. You can change the "Home library" and "Current library" when editing items and thus lock yourself out of your own items accidentally. -- This sounds like a bug to me.