Help apt-cache policy

[lc <redbliss@alice.it>]

The command apt-cache policy gives 2 answers:
for example:

~# apt-cache policy wxmaxima
wxmaxima:
  Installed: 0.7.1-1
  Candidate: 0.8.2-1
  Version table:
     0.8.2-1 0
        700 http://ftp.it.debian.org unstable/main Packages
 *** 0.7.1-1 0
        100 /var/lib/dpkg/status

why this happens? who created and updates the status list?
How can I have only 1 syncronized list?
I use unstable and experimental

thanks