They are celebrating something that hasn't been finished properly.
It is a very complicated story but the unification of west and east Germany didn't go by the book. Kohl claimed that the unification only could take
place if the land that was taken by Poland should remain Polish. Gorbatchev stated later in an interview that that was never a demand. There is also
no official peace treaty, only the so called "2+4 treaty" (see link below). There are many more issues, one of them is being discussed in the related
thread I luckily found here on ATS. This stuff needs really some attention.
translate.google.com
(visit the link for the full news article)

