The size limit was removed because it caused more problems then it solved. It seems that the documentation image is out of date.
If the item is disappearing when you add a new identical one it must be an issue of how you add the new item.
Are you using an Item Action to Equip or perhaps an Drag&Drop Action?
Check that you are using the correct method to add the item to be equipped.
For an Item Action I would use the "Move To Collection Item Action"
For the Drag&Drop I would use the ContainerSmartExchange
You can learn more about those in the documentation.
Essentially you want to remove the item from both the default and equipped collection before adding them to the opposite collection. This is all done automatically when using the SmartExchange or the MoveToCollection item action.
Of course if you want to have more control you can create your own custom item Action of Drag&Drop Action. You can learn how in the documentation and use the built-in actions as examples.
If you want even more control you can create your own custom ItemCollection but that should not be necessary for this use case.
I hope this helps