apt-get will upgrade aptitude will not

[Bonno Bloksma <b.bloksma@tio.nl>]

Hi,

On 2 of my machines I have mysql-common installed

# aptitude show mysql-common
Package: mysql-common
State: installed
Automatically installed: no
Version: 5.1.49-3
Priority: optional
Section: database
[....]

However, now apt-get wants to install an update but aptitude will not.

# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  mysql-common
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 69.6 kB of archives.
After this operation, 57.3 kB disk space will be freed.
Do you want to continue [Y/n]? n
Abort.

# aptitude upgrade
No packages will be installed, upgraded, or removed.
0 packages upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
Need to get 0 B of archives. After unpacking 0 B will be used.

What gives? The same is happening when I use aptitude safe-upgrade, as it should I suppose. ;-)
Of course I can simply use apt-get but I also want to understand what is going on.

Bonno Bloksma