Fantastic!
2 Things I am curious about after this update.
1. I am not sure if this is what you were referencing with "backwards compatibility issues" with projects made pre 1.2. When I create a new collection and go to select my custom property, I am seeing the GUID instead of the name of the Custom Property.
2. Will there ever be a way to edit the collection to "verify" which property it is a collection of? I understand for the most part you should be able to look at it and know, but is a quality of life thing to quick verify.
Example:
Keep up the GREAT work!