FusionDrive + Encrypted CoreStorage Volume - Problems writing to volume Has anyone had experience with encrypted (home made!) FusionDrive volumes and intermittent failure of writes to this disk?

I'm on a Late 2011 MBP 13" with (currently) 4 GB RAM, a 128 GB SSD and a 750 GB SATA disk.

When I'm trying to rsync data (from a TM backup) onto it, I get write failures.  I also could not successfully decrypt the volume when I tried.

I have stress tested the disks and they seem fine, and checked RAM, so other than a fault with the drive controller, which I doubt, I don't think it's a hardware problem.

Can anyone post success or similar failures with this kind of setup?
It happens to me when I have the SSD at the second bay, all was fixed when I put the SSD at the main bay in order to be shown as disk0