Do they disappear as soon as you re-enter a game or ?

No actually, some can last large amounts of time. They can last anywhere from the second you go into a new game to months I'm sure.

Here is a guide explaining 'unperms' and 'dupes' http://forums.d2jsp.org/topic.php?t=17431073&f=21

This post was edited by hphman1193 on Jun 11 2011 03:54pm

Thought so :-/

thx m8.