In the future, you may wish to go into synaptic's preferences and unmark the box that says to include recommended packages as dependencies. Perhaps the upgrade of kde only recommended the upgrade of Xorg, but was included as a dependency due to the preference choice. Also, you can go into preferences and ask that synaptic not automatically delete old packages after new ones are installed, but rather save them to a cache. Another option within synaptic is to force a version of a particular package. If you save it to a cache, I would guess it will appear as an option for the force in the drop-down selection.
http://www.linuxjournal.com/article/7034