aptitude ignores preferences files in /etc/apt/preferences.d/

[z0d]

Under Ubuntu 10.10, I created a file "/etc/apt/preferences.d/ubuntu-x-swat-ppa-nvidia" (attached) containing pinning preferences for apt. apt-get honours my preferences, offering me updates to the nvidia packages only (I don't have or want ATI or Intel driver updates). aptitude (and synaptic), however, only honours my preferences file if I move it to "/etc/apt/preferences". I expect aptitude (and synaptic) to honour my pinning preferences, whether they are stored in the "/etc/apt/preferences" file or their own file in "/etc/apt/preferences.d/".

$ sudo vi /etc/apt/preferences.d/ubuntu-x-swat-ppa-nvidia

$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

$ sudo aptitude upgrade
The following packages will be upgraded:
  fglrx-modaliases intel-gpu-tools libdrm-intel1 libdrm-nouveau1 libdrm-radeon1 libdrm2
  xserver-xorg-video-ati xserver-xorg-video-intel xserver-xorg-video-radeon
9 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 998kB of archives. After unpacking 32.8kB will be used.
Do you want to continue? [Y/n/?] n
Abort.

$ sudo mv /etc/apt/preferences.d/ubuntu-x-swat-ppa-nvidia /etc/apt/preferences

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

$ lsb_release -rd
Description: Ubuntu 10.10
Release: 10.10

$ apt-cache policy apt aptitude synaptic
apt:
  Installed: 0.8.3ubuntu7.1
  Candidate: 0.8.3ubuntu7.1
  Version table:
 *** 0.8.3ubuntu7.1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     0.8.3ubuntu7 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick/main amd64 Packages
aptitude:
  Installed: 0.6.3-2ubuntu4
  Candidate: 0.6.3-2ubuntu4
  Version table:
 *** 0.6.3-2ubuntu4 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick/main amd64 Packages
        100 /var/lib/dpkg/status
synaptic:
  Installed: 0.63.1ubuntu14
  Candidate: 0.63.1ubuntu14
  Version table:
 *** 0.63.1ubuntu14 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick/main amd64 Packages
        100 /var/lib/dpkg/status