We have encountered a problem with blkid that is caused by cryptsetup 
not cleaning superblocks of old filesystems on luksFormat. The problem 
has been fixed in 1.0.7, however old LUKS volumes still suffer from this 
problem. Please read this thread for details:

http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/2563

What I would request is an option to "clean" the unused area in the LUKS 
header up to the start of the payload, such that for example an old ext2 
magic is removed. All that without destroying the used areas in the LUKS 
header, of course.

I'm not very familiar with the LUKS code or on-disk format, so I would 
be greatful if anyone who is would implement such a feature. Thanks for 
your replies.

Thomas