I have a custom component on a block that uses the _ContextMixin as described in the following link
If I create a new block the context describes the block where the property exists as expected.
If I, on the other hand, have a page with a ContentArea and clicks the "Create a new block" link on that content area, the context returned is not the block context but the page context where the ContentArea is located.
Seems like a bug. You should probably report it to Epi.
Already done, but they need a working code sample based on their alloy sample so I have to write such an example to get any further.... Frustrating....
Problem can be reproduced by the AlloyDemoKit fork at