The instance properties are stored in the instance. So if you delete it, those properties are gone.
When you create a new instance, Construct will copy the properties of an arbitrary existing instance. If none exist, it will try to use the properties of any previously deleted instance. If there are still none, you get the defaults.
So the properties you get depend on whether there are other instances in the project, or whether you previously deleted instances.
I think there might be a small inconsistency in how behavior properties are handled though, they don't seem to refer back to deleted instances. I'll look in to that a bit further.