I have seen this too. Not only a past disfellowshipping but even minor things and also gossip and rumors are held against the person indefinitely and follow him/her to their next congregation.
Witnesses are conditioned to look at the bad in each person so they can tell them how much "they" (the other person) need the kingdom. Other religions teach to look for the good in others and build on it.
I knew of an elderly couple, (couple A) now deceased, who were baptized in 1950 (before I was born!) Shortly thereafter they witnessed to their friends (couple B). couple B also got baptized. Later on Couple A became inactive for many years. When I met them they had just returned and were active in the congregation, and remained so till their deaths. But behind their backs Couple B always made comments like, "Well I never fell away or had any doubts, not for one second. I was always completely faithful.." I always LOVED to use the scriptures on them (couple B) about being "faithful in what is least" and "gadding about, talking of things they ought not..."