Mismatch of packages to be updated between Update Manager (gui) and apt-get(cli)

I noticed my system acting weird today. While the update manager (gui application) states that there are 14 updates selected, and 52 Mb will be downloaded, the apt-get upgrade command only informs me of 1 update to be downloaded and installed.

The Update Manager Gui (output) can be found here:

and the cli apt-get upgrade output here:

fokis@fokis-netbook:~$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages have been kept back:
  ginn libgrip0 linux-generic linux-headers-generic linux-headers-generic-pae
  linux-image-generic
The following packages will be upgraded:
  linux-libc-dev
1 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.
Need to get 866 kB of archives.
After this operation, 2,048 B of additional disk space will be used.
Do you want to continue [Y/n]? n
Abort.

Note: I have run apt-get update before apt-get upgrade in the command line.

What is it that I am doing wrong?

From the CLI output you can see that some packages have been kept back, such as new kernel versions/headers. While update-manager installs them by default, apt-get requires the dist-upgrade parameter to include such packages in its upgrades.

Technically, apt-get upgrade will not install any new packages, e.g. linux-image-..., while dist-upgrade will. For more information on the differences between upgrade and dist-upgrade see here.