If you have a very brief post, clicking below the post no longer deselects the block:

This is likely a regression from the inline metaboxes. Previously the block container was at minimum 100% tall, meaning you could always click below the blocklist on short posts. Now it can't be 100% tall because there can be metaboxes:

The problem, likely, is that it's the block container that registers clicks as de-selects. Should we expand that so clicking anywhere outside the block itself deselects it?