I've been trying to optimize my website and I've discovered that using stacks on the page will prevent full-page caching when using the "if all blocks support it" option. This is the case even if the stack does not contain any blocks at all and is completely empty.

Is this a bug or by-design? Is there a way to allow stacks to cache?

On a related note: is there a way to tell which block is preventing caching? It took me quite a while to figure out why caching wasn't working.