This bug was initially created as a copy of Bug #1772531

I am copying this bug because: we need to add some warning in the documentation.

[RBD only bug] 

Creating a volume from a snapshot of an encrypted volume may result in an unusable volume.
Detectable only by looking at behaviour inside the instance upon attach.

Creating encrypted volume from a snapshot -created from a
source encrypted volume as well- will be forced to resize and  lose the encrypted header.

When creating an encrypted volume from a snapshot of an encrypted volume, if the amount
of data in the original volume at the time the snapshot was created is very close to the
gigabyte boundary given by the volume's size, it is possible for the data in the new
volume to be silently truncated.