I was in your exact same situation recently; I tried out Kubuntu for about a week, and was just starting to try out Korganizer/Kontact when I found the very bug you describe. I wanted to use Kontact to remind me of important dates, rent payments, and stuff like that, but the date I entered would always show up 2 days early.
I was pleasantly surprised to find the "Report bug" option under the Kontact "Help" menu. Clicking here took me almost effortlessly through the process of submitting a bug through the
proper channels.
I have already
filed the bug for this date problem, but nobody else has reported additional comments. You may be the first! But it does look like the bug has been assigned to someone, so with any luck it will be found and fixed in an upcoming minor release.
Also, I know this is not a Kubuntu bug, because I have since gone back to using Gentoo, and the Kontact/Korganizer bug is there also.