IMHO this could be by design. As "create" operation will try to create local block that resides in "For this page" assets folder. Can't remember if local assets folder is applicable for blocks. Might be that you are hitting just design limitation here.
I have a Page Type,
One of its properties is a ContentArea, in the Episerver back office I can create a new block or drag one in - No problems here.
However I created a block type that contains a ContentArea.
When I put this block into the content area of the page then go to edit that block, I can see the ContentArea inside the block but instead of showing:
"You can drop content here, or create a new block"
It just says "You can drop content here" with out the link to then create the Block that goes inside the block (hope that's clear)
Any one know why Episerver would do this, I have never seen a ContentArea in the back office that dosn't have that create new block link as an option.
Thanks in advance.
Ayo