Exactly. Cryptsetup wouldn't know about the extra copy of the volume key in kernel memory. Which is why, dramatically, it appeared secure ("surely I wouldn't be asked to resupply the passphrase if the volume key is still in memory, right?").

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pedrocr an hour ago | parent [-]

It was still more secure than the default if I understand this correctly. On resume from suspend the laptop would still be locked by the encryption key and without access to the disk even if you can somehow circumvent the lock. The only insecurity was that somewhere in the kernel memory the key still exists so if you can somehow extract that from the live system you can unlock it.

	▲	IngoBlechschmid an hour ago \| parent [-]
		Yes, you are right: LUKS encryption protests your data at rest. An attacker which steals your disk can only gain little, like the information that you have used LUKS (unless you put your LUKS headers elsewhere, separated from the disk) and perhaps disk and disk sector usage statistics.