The explanation for the quote nesting setting in the ACP should probably be reworded. Currently, it's:

Maximum nested quotes per post:
Maximum number of nested quotes in a post. Set to 0 for unlimited depth.

The setting is really per quote-block and not per post. So something like this would be more accurate:

Maximum nesting depth for quotes:
Maximum quote nesting depth in a post. Set to 0 for unlimited depth.

~line 180/181 of /language/en/acp/board.php