Yum update problem with %preun

[lluis]

I am trying to the yum update command using a spec file with pre,post
and %preun

Yum does not correctly update my package:

It starts with the %pre then %post of the new package version, and after
that do the %preun of the old package version!

At the end the package is not correctly installed because of %preun
commands (unlinks, etc )

Does Somebody experienced this problem ?
What's wrong in my package ? 

Thank.