We apologize for the Key confusion. When a friend borrows an item it doesn't remove your Keys. You actually earn Keys when a friend borrows from you!

Please note the following below:

1. You can borrow one Inventory item per day. You cannot borrow the same item from the same friend more than once. 
2. You or your friends cannot borrow Diamonds, Keys, or Cash.
3. You can borrow from the same friend once per three days.
4. Borrowing does not deduct a use of the borrowed item from your friend or your own Inventory.
5. You will earn 3 Keys for each item borrowed from you and receive a notification when this occurs.

When you open Design Home and see this notification the Keys have already been added to your currency at the top of the page so you will not see them change.