After changing the custome template settings on a block - in the demo install results in the block no longer being editable until the page is published and edited again.

I hope this is a bug.

Feedback is provided after the change via the "Design Updated" Green flyout then the user is leftclicking about trying to work out how to keep making changes. The only option it to look at the green edit pencil and wonder if this is the way to go.

Publish changes or discard? That's the options at this point. No choice to choose another custom template without saving or discarding.