There's no way as far as I can see of knowing where a block originally came from.

This causes problems for theming and styling, as you get CSS classes 'block-blockcache' and ID 'block-blockcache-DELTA'.

This could probably be fixed by adding this the the block array in blockcache_block_rebuild() and then providing a block-blockcache.tpl.php in the module that outputs these as extra CSS classes.