Poser hasn`t been completely rewritten since version 2 AFAIK.

According to posts of people who do have poser 6, there are quite a few bugs and some of them are major, a lot of these bugs were not in p4 or earlier.

There are quite a few design flaws.

Not being able to copy and paste parameters is a problem I have been suggesting they fix since poser 4, it would help a lot in figure creation and editing.