Comment 112 for bug 261721

The reason 2.6.27-13 isn't automatically installed is that, for some strange reason, linux-image-generic wasn't updated, and still points to -12...

To see this for yourself, run "aptitude why linux-image-2.6.27-12-generic", and it will tell you that it's automatically installed because you have installed linux-image-generic. Then do "aptitude show linux-image-generic, and it will tell you it depends on 2.6.27-12