I was trying to include few of my entities in custom extension. The workflow is easy:
Create Thing -> Add Subscription (me:ThingStart) -> Export as Source Control Entities -> Add to Entities folder in extension sources -> Try to import extension -> ERROR
Attribute 'sourceType' is not allowed to appear in element 'Subscription'.
In MyEntity.xml file there is actually this attribute: sourceType: Thing.
After deleting it it is working perfectly.
It's bug or I'm missing something?
This is a known issue reported to our R&D team with the ID TW-26125. Hope this helps for the moment.