I had the same problem on Lenny with a VPS Machine. Create a new deb-package solve the problem.
Now there is a new problem:
'apt-get upgrade' wants to reinstall pure-ftpd-mysql. If i do this, i get the version with capabilities on. ISPConfig3 also give me a warning. What can i do? Is there a way to disable lookup for pure-ftpd-mysql in dpkg?
Problem solved. I must set the package on hold in dpkg. Now there are no warnings in apt-get and ISPConfig3.
echo pure-ftpd-mysql hold | dpkg --set-selections