Changing z order in the editor changes the iid of an instance.
Attach a Capx
Description of Capx
Shows that iid is changed with z order
Steps to Reproduce Bug
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Closing as won't fix. IIDs are not constant and should not be relied on like that. Use UIDs instead.
But why should changing the z change the iid?
Because the initial objects placed in the layout happen to be created in order of their Z order. You shouldn't rely on what order the editor happens to assign IIDs, they swap and change even at runtime as objects create and destroy; UIDs are there to be permanent references.
The runtime change is quite exploitable for instances, as long as the change is predictable.
Uid on the other hand, is not.
Well at least keep it in mind for C3 please.