Ashley
(Note: By "default instance" I mean the very first instance of an object type created for the project - the template that future instances inherit all of their properties from, not the first instance in a given layout or having an IID of 0.)
Basically there's no way of knowing which instance is the default, nor where it's located if you want to change its properties (unless objects are stored in a separate dedicated layout, but sometimes you forget to do so). We also don't have any way of changing which instance is the default, which in some cases automatically changes behind-the-scenes.
So I propose we get a "Make Default Instance" button in the object properties. When it is clicked, all future instances will inherit the properties of this instance. A small label at the top of the object properties saying "Default Instance" or "Template" or something would be very nice as well.
This will also let us work around the bug where new tilemap instances inherit the placed tiles from a previous instance instead of the blank default instance. (I meant to report it but found it difficult to reproduce; seems to just happen over time.)