Comment 3 for bug 1506139

Well, life would be much easier if there was some usable documentation about what's going on within systemd.

By the way, I did not put in that 'swap' option manually, it was inserted by the xubuntu 15.10 beta installer on cdrom/usb image. If you choose to encrypt a partition and put a swap inside, it automatically adds that swap option. So at least this crypttab option, the behaviour of the installer, and systemd don't fit together.

Since you mention it: On my other machine with 15.10 I noticed the problem that the machine does not recover from hibernate, but performs a fresh boot, which meets your hint, that wake up does not work with that style of crypt swap.

whatever it is what fills the device with random data, should honor the luks option in the crypttab and use this thing as intended (i.e. configure the device mapper and do a swapon).