CoreStorage encryption fails - Is it possible to have multiple encrypted partitions on an external drive?

I have a 2TB WD MyBook Studio drive connected via FireWire to my MBP. What I would like to have is two encrypted partitions. So what I do: Disk Utility > Partition and then right click on each partitions and say "Encrypt Volume".

However, the procedure always fails, once the second partition is encrypted. I get really strange behavior in OS X. Disks will stop encrypting, get awfully slow and the whole system becomes unresponsive. I tried multiple times with OS X 10.8.6 and also 10.10.1.

So I am wondering if the issue is related to the WD disk somehow or if it is a limitation of CoreStorage that only one volume per disk can be encrypted. Do you have any experience with this? Any hints where I could continue looking?